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Vertical Gallium Oxide Isolated Source Electrode Field Effect Transistors (ISEFET) Without Planarization or Mid-Gap Acceptor Blocking Layers
Authors:
Akilesh Srikanth,
Md Saklain Morshed,
Chandan Joishi,
Ahmad E. Islam,
Siddharth Rajan
Abstract:
We propose and demonstrate the first vertical Gallium oxide device architecture without the use of planarization etch back processes or mid-gap acceptor regions. The Isolated Source Electrode Field Effect Transistor (ISEFET) incorporates a dielectric blocking layer to access an isolated source pad extending from the top fin metal. Scaled multi-fin channels were formed by electron beam lithography…
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We propose and demonstrate the first vertical Gallium oxide device architecture without the use of planarization etch back processes or mid-gap acceptor regions. The Isolated Source Electrode Field Effect Transistor (ISEFET) incorporates a dielectric blocking layer to access an isolated source pad extending from the top fin metal. Scaled multi-fin channels were formed by electron beam lithography with a width of 200 nm along with the source pads and then etched to a trench depth of ~1.2 um. The fabricated devices showed enhancement mode operation with threshold voltage of 2 V and on-off ratio > 1e7 with excellent gate modulation characteristics. The resulting device proved to be comparable to existing vertical transistors and suitable for high-throughput prototyping and large-scale manufacturing of future Gallium oxide and other wide bandgap semiconductor devices.
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Submitted 13 August, 2026;
originally announced August 2026.
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AlN Gate Interlayer for UWBG AlGaN Transistors with Breakdown Field >6.9 MV/cm and PFOM >1.8 GW/cm2
Authors:
Seungheon Shin,
Jonathan Pratt,
Joe McGlone,
Yinxuan Zhu,
Brianna A. Klein,
Andrew Armstrong,
Andrew A. Allerman,
Siddharth Rajan
Abstract:
We report the demonstration of regrown epitaxial AlN gate interlayers with ultra-wide bandgap (UWBG) AlGaN polarization-graded field effect transistors (PolFETs). The introduction of the epitaxial AlN gate interlayer enables significant improvement in breakdown strength, with average breakdown field exceeding 6.94 MV/cm, which represents state-of-the-art for lateral field effect transistors, while…
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We report the demonstration of regrown epitaxial AlN gate interlayers with ultra-wide bandgap (UWBG) AlGaN polarization-graded field effect transistors (PolFETs). The introduction of the epitaxial AlN gate interlayer enables significant improvement in breakdown strength, with average breakdown field exceeding 6.94 MV/cm, which represents state-of-the-art for lateral field effect transistors, while maintaining excellent on-state current density exceeding 1 A/mm. The integration of epitaxial AlN enables state-of-the-art power-switching figure of merit exceeding 1.87 GW/cm2 at a breakdown voltage exceeding 1.45 kV. This work shows the potential of UWBG AlGaN for next-generation high-power switching and RF applications with enhanced device performance established by a high-quality epitaxially regrown AlN gate interlayer.
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Submitted 1 June, 2026;
originally announced June 2026.
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High Breakdown Field Multi-kV UWBG AlGaN Transistors
Authors:
Seungheon Shin,
Kyle Liddy,
Jon Pratt,
Can Cao,
Yinxuan Zhu,
Brianna A. Klein,
Andrew Armstrong,
Andrew A. Allerman,
Siddharth Rajan
Abstract:
We demonstrate high-performance UWBG AlGaN PolFETs exhibiting a state-of-the-art combination of nearly 1 A/mm on-state current (~ 960 mA/mm) and large breakdown field (> 4.8 MV/cm) in high carrier density (1.15 x 1013 cm-2). Multi-kV robustness is successfully demonstrated exhibiting 1.28 and 2.17 kV by utilizing a gate-connected field plate structures in 3.9 and 6.8 μm LGD, corresponding to the e…
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We demonstrate high-performance UWBG AlGaN PolFETs exhibiting a state-of-the-art combination of nearly 1 A/mm on-state current (~ 960 mA/mm) and large breakdown field (> 4.8 MV/cm) in high carrier density (1.15 x 1013 cm-2). Multi-kV robustness is successfully demonstrated exhibiting 1.28 and 2.17 kV by utilizing a gate-connected field plate structures in 3.9 and 6.8 μm LGD, corresponding to the extremely low specific on-resistance of 1.25 and 2.86 mΩcm2, respectively. High RF performance is also achieved, providing fT and fMAX, of 8.5 and 15 GHz, respectively, for 3.9 μm LGD. These results highlight UWBG AlGaN as a platform for both high-voltage RF and power applications.
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Submitted 7 April, 2026;
originally announced April 2026.
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Electrostatic Effects of Self Trapped Holes in Gallium Oxide Devices
Authors:
Nathan Wriedt,
Joe McGlone,
Davide Orlandini,
Siddharth Rajan
Abstract:
Gallium oxide is an ultra-wide bandgap semiconductor with exceptional properties for power electronics and UV-C optoelectronics, but its behavior under illumination remains poorly understood. In this work, we investigate how optically generated self-trapped holes influence electrostatics and current conduction in gallium oxide devices. Using a vertical Schottky photodiode with a semi-transparent N…
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Gallium oxide is an ultra-wide bandgap semiconductor with exceptional properties for power electronics and UV-C optoelectronics, but its behavior under illumination remains poorly understood. In this work, we investigate how optically generated self-trapped holes influence electrostatics and current conduction in gallium oxide devices. Using a vertical Schottky photodiode with a semi-transparent Ni anode, we performed capacitance-voltage, current-voltage, and temperature-dependent I-V measurements under dark and above-bandgap illumination. Analysis of photocurrent gain reveals that conventional image-force barrier-lowering models require unrealistically high interfacial electric fields, suggesting the presence of an alternative mechanism. By applying Fowler-Nordheim tunneling theory, we reconcile measured photocurrents and photo-capacitance results with physically plausible fields and quantify the two-dimensional concentration of self-trapped holes. Our findings demonstrate that illumination-induced charge significantly alters device electrostatics. Understanding this tunneling-based photocurrent gain mechanism is critical for designing gallium oxide devices for UV-C detectors and power electronics.
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Submitted 27 March, 2026;
originally announced March 2026.
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Extremely Low Thermal Resistance Architectures for AlxGaN1-x Semiconductor Devices
Authors:
Kidus Guye,
Davide Orlandini,
Seungheon Shin,
Andy Allerman,
Damena Agonafer,
Siddharth Rajan,
Samuel Graham
Abstract:
Next-generation high-power radio-frequency (RF) devices increasingly demand transistors that operate efficiently with high gain at high frequencies. High-aluminum-content ultra-wide-bandgap (UWBG) AlGaN alloys have shown great potential for enabling such high-frequency RF technologies. However, the widespread adoption of AlGaN-based RF devices is limited by thermal-management challenges arising fr…
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Next-generation high-power radio-frequency (RF) devices increasingly demand transistors that operate efficiently with high gain at high frequencies. High-aluminum-content ultra-wide-bandgap (UWBG) AlGaN alloys have shown great potential for enabling such high-frequency RF technologies. However, the widespread adoption of AlGaN-based RF devices is limited by thermal-management challenges arising from the intrinsically low thermal conductivity of AlGaN, which leads to higher device thermal resistance for a given geometry compared to GaN RF devices. As a result, these next-generation devices are highly susceptible to self-heating. This study investigates the thermal behavior of UWBG AlGaN devices, focusing on the effects of AlGaN channel thickness, substrate technology, and high-k material integration on reducing device thermal resistance to enable high-power operation. Experimental results demonstrate a record-low thermal resistance of 3.96 mm$\cdot$K/W when an AlN substrate is employed and the AlGaN channel thickness is reduced to 5 nm. These findings provide valuable insights into mitigating thermal limitations in UWBG devices through device-level engineering and the strategic integration of high-k materials.
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Submitted 21 February, 2026;
originally announced February 2026.
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Social Contagion and Bank Runs: An Agent-Based Model with LLM Depositors
Authors:
Chris Ruano,
Shreshth Rajan
Abstract:
Digital banking and online communication have made modern bank runs faster and more networked than the canonical queue-at-the-branch setting. While equilibrium models explain why strategic complementarities generate run risk, they offer limited guidance on how beliefs synchronize and propagate in real time. We develop a process-based agent-based model that makes the information and coordination la…
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Digital banking and online communication have made modern bank runs faster and more networked than the canonical queue-at-the-branch setting. While equilibrium models explain why strategic complementarities generate run risk, they offer limited guidance on how beliefs synchronize and propagate in real time. We develop a process-based agent-based model that makes the information and coordination layer explicit. Banks follow cash-first withdrawal processing with discounted fire-sale liquidation and an endogenous stress index. Depositors are heterogeneous in risk tolerance and in the weight placed on fundamentals versus social information, communicating on a heavy-tailed network calibrated to Twitter activity during March 2023. Depositor behavior is generated by a constrained large language model that maps each agent's information set into a discrete action and an optional post; we validate this policy against laboratory coordination evidence and theoretical benchmarks. Across 4,900 configurations and full LLM simulations, three findings emerge. Within-bank connectivity raises the likelihood and speed of withdrawal cascades holding fundamentals fixed. Cross-bank contagion exhibits a sharp phase transition near spillover rates of 0.10. Depositor overlap and network amplification interact nonlinearly, so channels weak in isolation become powerful in combination. In an SVB, First Republic, and regional bank scenario disciplined by crisis-era data, the model reproduces the observed ordering of failures and predicts substantially higher withdrawal rates among uninsured depositors. The results frame social correlation as a measurable amplifier of run risk alongside balance-sheet fundamentals.
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Submitted 13 February, 2026;
originally announced February 2026.
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Scaled Ultra-Wide Bandgap AlGaN Polarization-Graded FET with Ultra-thin Buffer Layer
Authors:
Yinxuan Zhu,
Ashley Wissel-Garcia,
Kidus Guye,
Chandan Joishi,
Can Cao,
Seungheon Shin,
Kyle Liddy,
Emils G. B. Jurcik,
Agnes Maneesha Dominic Merwin Xavier,
Andrew A. Allerman,
Brianna A. Klein,
Andrew Amrstrong,
James S. Speck,
Samuel Graham,
Siddharth Rajan
Abstract:
We report on the design and demonstration of ultra-wide bandgap AlGaN polarization-graded field effect transistors with ultra-thin channels to enable excellent current density and high-frequency performance while significantly reducing thermal resistance. We use polarization-graded AlGaN layers and ultra-thin pseudomorphic AlGaN buffer layers to enable low thermal resistance and excellent structur…
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We report on the design and demonstration of ultra-wide bandgap AlGaN polarization-graded field effect transistors with ultra-thin channels to enable excellent current density and high-frequency performance while significantly reducing thermal resistance. We use polarization-graded AlGaN layers and ultra-thin pseudomorphic AlGaN buffer layers to enable low thermal resistance and excellent structural quality. The polarization-graded field effect transistors (PolFETs) demonstrated here show Imax over 800mA/mm and current/power gain cutoff frequency (fT/fmax) of 26/28 GHz. Small signal modeling and analysis were used to determine parasitic/transit delays, and gate-resistance thermometry was implemented to thermally characterize AlGaN PolFET and benchmark against state-of-the-art AlGaN HEMTs. The ultra-thin AlGaN PolFET showed thermal resistance of 12 K.mm/W, representing a significant reduction from typical AlGaN transistors. These results show state-of-art combination of high current density, excellent fT-LG product for ultra-wide bandgap AlGaN transistors, and superior thermal performance, and highlight the promise of AlGaN transistors for future RF and mm-wave applications.
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Submitted 19 December, 2025;
originally announced December 2025.
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Ultra-Wide Bandgap AlGaN Heterostructure Field Effect Transistors with Current Gain Cutoff Frequency Above 85 GHz
Authors:
Yinxuan Zhu,
Andrew A. Allerman,
Ashley Wissel-Garcia,
Seungheon Shin,
Jon Pratt,
Can Cao,
Kyle J. Liddy,
James S. Speck,
Brianna A. Klein,
Andrew Armstrong,
Siddharth Rajan
Abstract:
We report the design and demonstration of ultra-wide-bandgap (UWBG) AlGaN polarization-graded field-effect transistors (PolFETs) that achieve a current-gain cutoff frequency above 85 GHz and a current density exceeding 1.3 A/mm. Ultra-thin channel and buffer layers were grown epitaxially on AlN substrates, and a reverse-graded AlGaN contact layer was incorporated to reduce the contact resistance t…
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We report the design and demonstration of ultra-wide-bandgap (UWBG) AlGaN polarization-graded field-effect transistors (PolFETs) that achieve a current-gain cutoff frequency above 85 GHz and a current density exceeding 1.3 A/mm. Ultra-thin channel and buffer layers were grown epitaxially on AlN substrates, and a reverse-graded AlGaN contact layer was incorporated to reduce the contact resistance to below 1 ohm.mm. With aggressively scaled device dimensions, the AlGaN PolFETs exhibit state-of-the-art high-frequency performance for UWBG transistors. Small-signal modeling reveals both parasitic and transit delays, confirming the benefits of reduced access resistance and enhanced intrinsic transconductance. These results establish a new performance benchmark for UWBG AlGaN devices and demonstrate their strong potential for next-generation millimeter-wave electronics.
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Submitted 19 December, 2025;
originally announced December 2025.
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Barrier Electrostatics and Contact Engineering for Ultra-Wide Bandgap AlGaN HFETs
Authors:
Seungheon Shin,
Can Cao,
Jon Pratt,
Yinxuan Zhu,
Brianna A. Klein,
Andrew Armstrong,
Andrew A. Allerman,
Siddharth Rajan
Abstract:
We report ultra-wide bandgap (UWBG) AlGaN heterostructure field-effect transistors (HFETs) exhibiting a high breakdown field (> 5.3 MV/cm) and a low contact resistance (~1.55 Ωmm), tailored for high-power radiofrequency applications. A split-doped barrier architecture, employing two distinct doping concentrations, is shown to enhance both the breakdown field and contact resistance. This design ena…
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We report ultra-wide bandgap (UWBG) AlGaN heterostructure field-effect transistors (HFETs) exhibiting a high breakdown field (> 5.3 MV/cm) and a low contact resistance (~1.55 Ωmm), tailored for high-power radiofrequency applications. A split-doped barrier architecture, employing two distinct doping concentrations, is shown to enhance both the breakdown field and contact resistance. This design enables a state-of-the-art combination of maximum drain current (487 mA/mm) and breakdown field, along with a high cutoff frequency of 7.2 GHz. These results demonstrate a viable pathway to push device performance toward the material limits while minimizing contact resistance in UWBG AlGaN HFETs, paving the way for next-generation high-power, high-frequency applications.
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Submitted 23 September, 2025; v1 submitted 19 September, 2025;
originally announced September 2025.
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SmartTrap: Automated Precision Experiments with Optical Tweezers
Authors:
Martin Selin,
Antonio Ciarlo,
Giuseppe Pesce,
Lars Bengtsson,
Joan Camunas-Soler,
Vinoth Sundar Rajan,
Fredrik Westerlund,
L. Marcus Wilhelmsson,
Isabel Pastor,
Felix Ritort,
Steven B. Smith,
Carlos Bustamante,
Giovanni Volpe
Abstract:
There is a trend in research towards more automation using smart systems powered by artificial
intelligence. While experiments are often challenging to automate, they can greatly benefit from
automation by reducing labor and increasing reproducibility. For example, optical tweezers are
widely employed in single-molecule biophysics, cell biomechanics, and soft matter physics, but they
still…
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There is a trend in research towards more automation using smart systems powered by artificial
intelligence. While experiments are often challenging to automate, they can greatly benefit from
automation by reducing labor and increasing reproducibility. For example, optical tweezers are
widely employed in single-molecule biophysics, cell biomechanics, and soft matter physics, but they
still require a human operator, resulting in low throughput and limited repeatability. Here, we
present a smart optical tweezers platform, which we name SmartTrap, capable of performing complex
experiments completely autonomously. SmartTrap integrates real-time 3D particle tracking using
deep learning, custom electronics for precise feedback control, and a microfluidic setup for particle
handling. We demonstrate the ability of SmartTrap to operate continuously, acquiring high-precision
data over extended periods of time, through a series of experiments. By bridging the gap between
manual experimentation and autonomous operation, SmartTrap establishes a robust and open source
framework for the next generation of optical tweezers research, capable of performing large-scale
studies in single-molecule biophysics, cell mechanics, and colloidal science with reduced experimental
overhead and operator bias.
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Submitted 8 May, 2025;
originally announced May 2025.
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High Breakdown Electric Field (> 5 MV/cm) in UWBG AlGaN Transistors
Authors:
Seungheon Shin,
Hridibrata Pal,
Jon Pratt,
John Niroula,
Yinxuan Zhu,
Chandan Joishi,
Brianna A. Klein,
Andrew Armstrong,
Andrew A. Allerman,
Tomás Palacios,
Siddharth Rajan
Abstract:
We report on the design and demonstration of ultra-wide bandgap (UWBG) AlGaN-channel metal-insulator heterostructure field effect transistors (HEFTs) for high-power, high-frequency applications. We find that the integration of gate dielectrics and field plates greatly improves the breakdown field in these devices, with state-of-art average breakdown field of 5.3 MV/cm (breakdown voltage > 260 V) w…
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We report on the design and demonstration of ultra-wide bandgap (UWBG) AlGaN-channel metal-insulator heterostructure field effect transistors (HEFTs) for high-power, high-frequency applications. We find that the integration of gate dielectrics and field plates greatly improves the breakdown field in these devices, with state-of-art average breakdown field of 5.3 MV/cm (breakdown voltage > 260 V) with an associated maximum current density of 342 mA/mm, and cut-off frequency of 9.1 GHz. Furthermore, low trap-related impact was observed from minimal gate and drain lag estimated from pulsed I-V characteristics. The reported results provide the potential of UWBG AlGaN HEFTs for the next generation high-power radio frequency applications.
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Submitted 17 April, 2025; v1 submitted 17 April, 2025;
originally announced April 2025.
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Energy Bands and Breakdown Characteristics in Al2O3/UWBG AlGaN Heterostructures
Authors:
Seungheon Shin,
Kyle Liddy,
Yinxuan Zhu,
Chandan Joishi,
Brianna A. Klein,
Andrew Armstrong,
Andrew A. Allerman,
Siddharth Rajan
Abstract:
We report on energy bands and breakdown characteristics of Al2O3 dielectrics on ultra-wide bandgap (UWBG) AlGaN heterostructures. Metal-dielectric-semiconductor structures are important to sustain high fields needed for future high-performance UWBG transistors. Using systematic experiments, we determined the fixed charge density (> 1013 cm-2), the dielectric/interface, and electric fields in the o…
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We report on energy bands and breakdown characteristics of Al2O3 dielectrics on ultra-wide bandgap (UWBG) AlGaN heterostructures. Metal-dielectric-semiconductor structures are important to sustain high fields needed for future high-performance UWBG transistors. Using systematic experiments, we determined the fixed charge density (> 1013 cm-2), the dielectric/interface, and electric fields in the oxide of under flat-band conditions in the semiconductor. Low gate-to-drain leakage current of up to 5 x 10-7 A/cm2 were obtained in the metal-oxide-semiconductor structures. In lateral metal-semiconductor-insulator test structures, breakdown voltage exceeding 1 kV was obtained with a channel sheet charge density of 1.27 x 1013 cm-2. The effective peak electric field and average breakdown field were estimated to be > 4.27 MV/cm and 1.99 MV/cm, respectively. These findings demonstrate the potential of Al2O2 integration for enhancing the breakdown performance of UWBG AlGaN HEMTs.
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Submitted 17 April, 2025; v1 submitted 1 April, 2025;
originally announced April 2025.
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Impact of Quantum Well Thickness on Efficiency Loss in InGaN/GaN LEDs: Challenges for Thin-Well Designs
Authors:
Xuefeng Li,
Nick Pant,
Sheikh Ifatur Rahman,
Rob Armitage,
Siddharth Rajan,
Emmanouil Kioupakis,
Daniel Feezell
Abstract:
We investigate the impact of quantum well (QW) thickness on efficiency loss in c-plane InGaN/GaN LEDs using a small-signal electroluminescence (SSEL) technique. Multiple mechanisms related to efficiency loss are independently examined, including injection efficiency, carrier density vs. current density relationship, phase space filling (PSF), quantum confined stark effect (QCSE), and Coulomb enhan…
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We investigate the impact of quantum well (QW) thickness on efficiency loss in c-plane InGaN/GaN LEDs using a small-signal electroluminescence (SSEL) technique. Multiple mechanisms related to efficiency loss are independently examined, including injection efficiency, carrier density vs. current density relationship, phase space filling (PSF), quantum confined stark effect (QCSE), and Coulomb enhancement. An optimal QW thickness of around 2.7 nm in these InGaN/GaN LEDs was determined for quantum wells having constant In composition. Despite better control of deep-level defects and lower carrier density at a given current density, LEDs with thin QWs still suffer from an imbalance of enhancement effects on the radiative and intrinsic Auger-Meitner recombination coefficients. The imbalance of enhancement effects results in a decline in internal quantum efficiency (IQE) and radiative efficiency with decreasing QW thickness at low current density in LEDs with QW thicknesses below 2.7 nm. We also investigate how LED modulation bandwidth varies with quantum well thickness, identifying the key trends and their implications for device performance.
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Submitted 28 February, 2025;
originally announced February 2025.
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Electrical and Structural Properties of In-Situ MOCVD Grown Al$_2$O$_3$/$β$-Ga$_2$O$_3$ and Al$_2$O$_3$/$β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ MOSCAPs
Authors:
A F M Anhar Uddin Bhuiyan,
Lingyu Meng,
Dong Su Yu,
Sushovan Dhara,
Hsien-Lien Huang,
Vijay Gopal Thirupakuzi Vangipuram,
Jinwoo Hwang,
Siddharth Rajan,
Hongping Zhao
Abstract:
This study investigates the electrical and structural properties of MOSCAPs with in-situ MOCVD-grown Al$_2$O$_3$ dielectrics on (010) $β$-Ga$_2$O$_3$ and $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films. The Al$_2$O$_3$/$β$-Ga$_2$O$_3$ MOSCAPs showed a strong dependence on Al$_2$O$_3$ deposition temperature. At 900$^\circ$C, reduced voltage hysteresis ($\sim$0.3 V) and improved reverse breakdown voltage (74.…
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This study investigates the electrical and structural properties of MOSCAPs with in-situ MOCVD-grown Al$_2$O$_3$ dielectrics on (010) $β$-Ga$_2$O$_3$ and $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films. The Al$_2$O$_3$/$β$-Ga$_2$O$_3$ MOSCAPs showed a strong dependence on Al$_2$O$_3$ deposition temperature. At 900$^\circ$C, reduced voltage hysteresis ($\sim$0.3 V) and improved reverse breakdown voltage (74.5 V) were observed, with breakdown fields of 5.01 MV/cm in Al$_2$O$_3$ and 4.11 MV/cm in $β$-Ga$_2$O$_3$. At 650$^\circ$C, higher hysteresis ($\sim$3.44 V) and lower reverse breakdown voltage (38.8 V) were observed, with breakdown fields of 3.69 MV/cm in Al$_2$O$_3$ and 2.87 MV/cm in $β$-Ga$_2$O$_3$. However, forward breakdown fields improved from 5.62 MV/cm (900$^\circ$C) to 7.25 MV/cm (650$^\circ$C). STEM revealed improved crystallinity and sharper interfaces at 900$^\circ$C, enhancing reverse breakdown performance. For Al$_2$O$_3$/$β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ MOSCAPs, increasing Al composition ($x$ = 5.5\% to 9.2\%) reduced carrier concentration and improved reverse breakdown fields from 2.55 to 2.90 MV/cm in $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ and 2.41 to 3.13 MV/cm in Al$_2$O$_3$. Forward breakdown fields in Al$_2$O$_3$ improved from 5.0 to 5.4 MV/cm as Al composition increased. STEM confirmed compositional homogeneity and excellent stoichiometry of Al$_2$O$_3$ and $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ layers. These findings highlight the robust electrical performance, high breakdown fields, and structural quality of Al$_2$O$_3$/$β$-Ga$_2$O$_3$ and Al$_2$O$_3$/$β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ MOSCAPs for high-power applications.
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Submitted 22 May, 2025; v1 submitted 17 January, 2025;
originally announced January 2025.
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Selective-injection GaN Heterojunction Bipolar Transistors with 275 kA/cm$^2$ Current Density
Authors:
Zhanbo Xia,
Chandan Joishi,
Shahadat H. Sohel,
Andy Xie,
Edward Beam,
Yu Cao,
Siddharth Rajan
Abstract:
We design and demonstrate selective injection GaN heterojunction bipolar transistors that utilize a patterned base for selective injection of electrons from the emitter. The design maneuvers minority carrier injection through a thin p-GaN base region, while the majority carrier holes for base current are injected from thick p-GaN regions adjacent to the thin p-GaN base. The design is realized usin…
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We design and demonstrate selective injection GaN heterojunction bipolar transistors that utilize a patterned base for selective injection of electrons from the emitter. The design maneuvers minority carrier injection through a thin p-GaN base region, while the majority carrier holes for base current are injected from thick p-GaN regions adjacent to the thin p-GaN base. The design is realized using a regrowth emitter approach with SiO$_2$ as a spacer between the emitter layer and the thick p-GaN base contact regions. The fabricated device demonstrated state-of-art output current density (I$_{C, max}$) ~275 kA/cm$^2$ with a current gain ($β$) of 9, and 17 for the planar HBT design (I$_{C, max}$ =150 kA/cm$^2$). The reported results highlight the potential of the selective injection design to overcome the persistent GaN HBT design tradeoff between base resistance and current gain, paving the way for next-generation radio frequency and mm-Wave applications.
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Submitted 26 August, 2024;
originally announced August 2024.
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Active Interface Characteristics of Heterogeneously Integrated GaAsSb/Si Photodiodes
Authors:
Manisha Muduli,
Yongkang Xia,
Seunghyun Lee,
Nathan Gajowski,
Chris Chae,
Siddharth Rajan,
Jinwoo Hwang,
Shamsul Arafin,
Sanjay Krishna
Abstract:
There is increased interest in the heterogeneous integration of various compound semiconductors with Si for a variety of electronic and photonic applications. This paper focuses on integrating GaAsSb (with absorption in the C-band at 1550nm) with silicon to fabricate photodiodes, leveraging epitaxial layer transfer (ELT) methods. Two ELT techniques, epitaxial lift-off (ELO) and macro-transfer prin…
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There is increased interest in the heterogeneous integration of various compound semiconductors with Si for a variety of electronic and photonic applications. This paper focuses on integrating GaAsSb (with absorption in the C-band at 1550nm) with silicon to fabricate photodiodes, leveraging epitaxial layer transfer (ELT) methods. Two ELT techniques, epitaxial lift-off (ELO) and macro-transfer printing (MTP), are compared for transferring GaAsSb films from InP substrates to Si, forming PIN diodes. Characterization through atomic force microscopy (AFM), and transmission electron microscopy (TEM) exhibits a high-quality, defect-free interface. Current-voltage (IV) measurements and capacitance-voltage (CV) analysis validate the quality and functionality of the heterostructures. Photocurrent measurements at room temperature and 200 K demonstrate the device's photo-response at 1550 nm, highlighting the presence of an active interface.
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Submitted 26 July, 2024; v1 submitted 24 July, 2024;
originally announced July 2024.
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Tunnel Junction-Enabled Monolithically Integrated GaN Micro-Light Emitting Transistor
Authors:
Sheikh Ifatur Rahman,
Mohammad Awwad,
Chandan Joishi,
Zane-Jamal Eddine,
Brendan Gunning,
Andrew Armstrong,
Siddharth Rajan
Abstract:
GaN/InGaN microLEDs are a very promising technology for next generation displays. Switching control transistors and their integration are key components in achieving high-performance, efficient displays. Monolithic integration of microLEDs with GaN switching devices provides an opportunity to control microLED output power with capacitive (voltage) control rather than current controlled schemes. Th…
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GaN/InGaN microLEDs are a very promising technology for next generation displays. Switching control transistors and their integration are key components in achieving high-performance, efficient displays. Monolithic integration of microLEDs with GaN switching devices provides an opportunity to control microLED output power with capacitive (voltage) control rather than current controlled schemes. This approach can greatly reduce system complexity for the driver circuit arrays while maintaining device opto-electronic performance. In this work, we demonstrate a 3-terminal GaN micro-light emitting transistor that combines a GaN/InGaN blue tunneling-based microLED with a GaN n-channel FET. The integrated device exhibits excellent gate control, drain current control and optical emission control. This work provides a promising pathway for future monolithic integration of GaN FETs with microLED to enable fast switching high efficiency microLED display and communication systems.
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Submitted 29 May, 2024; v1 submitted 7 April, 2024;
originally announced April 2024.
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Design and Simulation of a III-Nitride Light Emitting Transistor
Authors:
Mohammad Awwad,
Sheikh Ifatur Rahman,
Chandan Joishi,
Betty Lise Anderson,
Siddharth Rajan
Abstract:
This paper describes the design and characteristics of monolithically integrated three-terminal gated III-Nitride light emitting diodes (LEDs) devices. The impact of channel doping and thickness on the voltage penalty of the transistor-LED hybrid device is analyzed, and it is shown that with appropriate design, low voltage drop can be realized across integrated gated LED structures. The impact of…
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This paper describes the design and characteristics of monolithically integrated three-terminal gated III-Nitride light emitting diodes (LEDs) devices. The impact of channel doping and thickness on the voltage penalty of the transistor-LED hybrid device is analyzed, and it is shown that with appropriate design, low voltage drop can be realized across integrated gated LED structures. The impact of device design on the switching charge is investigated, and it is shown that the adoption of an integrated LED/transistor structure can reduce the switching charge necessary for operation of a switched LED display device by an order of magnitude when compared with stand-alone light-emitting diodes.
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Submitted 7 April, 2024;
originally announced April 2024.
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Demonstration of a monocrystalline GaAs-$β$-Ga$_2$O$_3$ p-n heterojunction
Authors:
Jie Zhou,
Moheb Sheikhi,
Ashok Dheenan,
Haris Abbasi,
Jiarui Gong,
Yang Liu,
Carolina Adamo,
Patrick Marshall,
Nathan Wriedt,
Clincy Cheung,
Shuoyang Qiu,
Tien Khee Ng,
Qiaoqiang Gan,
Vincent Gambin,
Boon S. Ooi,
Siddharth Rajan,
Zhenqiang Ma
Abstract:
In this work, we report the fabrication and characterizations of a monocrystalline GaAs/$β$-Ga$_2$O$_3$ p-n heterojunction by employing semiconductor grafting technology. The heterojunction was created by lifting off and transfer printing a p-type GaAs single crystal nanomembrane to an Al$_2$O$_3$-coated n-type$β$-Ga$_2$O$_3$ epitaxial substrate. The resultant heterojunction diodes exhibit remarka…
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In this work, we report the fabrication and characterizations of a monocrystalline GaAs/$β$-Ga$_2$O$_3$ p-n heterojunction by employing semiconductor grafting technology. The heterojunction was created by lifting off and transfer printing a p-type GaAs single crystal nanomembrane to an Al$_2$O$_3$-coated n-type$β$-Ga$_2$O$_3$ epitaxial substrate. The resultant heterojunction diodes exhibit remarkable performance metrics, including an ideality factor of 1.23, a high rectification ratio of 8.04E9 at +/- 4V, and a turn on voltage of 2.35 V. Furthermore, at +5 V, the diode displays a large current density of 2500 A/cm$^2$ along with a low ON resistance of 2 m$Ω\cdot$cm$^2$.
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Submitted 5 October, 2023;
originally announced October 2023.
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Selective injection AlGaN/GaN heterojunction bipolar transistors with patterned regrown base contacts
Authors:
Chandan Joishi,
Sheikh Ifatur Rahman,
Zhanbo Xia,
Shahadat H. Sohel,
Siddharth Rajan
Abstract:
We demonstrate graded AlGaN/GaN heterojunction bipolar transistors (HBTs) with selective injection of minority carriers across a p-GaN base and patterned regrown base contacts. The selective injection design regulates minority carrier transport under emitter-base forward bias through a thin base region, while thick and highly doped p$^+$ GaN regrown layers patterned alongside the thin base regions…
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We demonstrate graded AlGaN/GaN heterojunction bipolar transistors (HBTs) with selective injection of minority carriers across a p-GaN base and patterned regrown base contacts. The selective injection design regulates minority carrier transport under emitter-base forward bias through a thin base region, while thick and highly doped p$^+$ GaN regrown layers patterned alongside the thin base regions are utilized to lower the base contact resistance. With SiO$_2$ employed as a spacer between the emitter and the p$^+$ regrown layers, the device with an interdigitated emitter/base-contact stripe design displayed a maximum collector current density (I$_C$) of 101 kA/cm$^2$, a maximum current gain ($β$) of 70 at I$_C$ $\sim$ 1 kA/cm$^2$ and $\sim$ 11 for I$_C$ $>$ 50 kA/cm$^2$. The reported results demonstrate the potential of the selective injection approach to break the long-existing HBT design tradeoff between base resistance and current gain for next-generation radio frequency and mm-Wave applications.
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Submitted 18 September, 2023;
originally announced September 2023.
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Initial demonstration of AlGaAs-GaAsP-beta-Ga2O3 n-p-n double heterojunctions
Authors:
Jie Zhou,
Ashok Dheenan,
Jiarui Gong,
Carolina Adamo,
Patrick Marshall,
Moheb Sheikhi,
Tsung-Han Tsai,
Nathan Wriedt,
Clincy Cheung,
Shuoyang Qiu,
Tien Khee Ng,
Qiaoqiang Gan,
Gambin Vincent,
Boon S. Ooi,
Siddharth Rajan,
Zhenqiang Ma
Abstract:
Beta phase gallium oxides, an ultrawide-bandgap semiconductor, has great potential for future power and RF electronics applications but faces challenges in bipolar device applications due to the lack of p-type dopants. In this work, we demonstrate monocrystalline AlGaAs_GaAsP_beta phase gallium oxides n-p-n double-heterojunctions, synthesized using semiconductor grafting technology. By transfer pr…
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Beta phase gallium oxides, an ultrawide-bandgap semiconductor, has great potential for future power and RF electronics applications but faces challenges in bipolar device applications due to the lack of p-type dopants. In this work, we demonstrate monocrystalline AlGaAs_GaAsP_beta phase gallium oxides n-p-n double-heterojunctions, synthesized using semiconductor grafting technology. By transfer printing an n-AlGaAs_p-GaAsP nanomembrane to the n-beta phase-Ga$_2$O$_3$ epitaxial substrate, we simultaneously achieved AlGaAs_GaAsP epitaxial n-p junction diode with an ideality factor of 1.29 and a rectification ratio of 2.57E3 at +/- 2 V, and grafted GaAsP_beta_phase_gallium oxides p-n junction diode exhibiting an ideality factor of 1.36 and a rectification ratio of 4.85E2 at +/- 2 V.
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Submitted 14 August, 2023; v1 submitted 12 August, 2023;
originally announced August 2023.
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Demonstration of Multi-Active Region P-down Green LEDs with High Quantum Efficiency
Authors:
Sheikh Ifatur Rahman,
Robert Armitage,
Siddharth Rajan
Abstract:
Longer wavelength emitters such as green LEDs display a pronounced efficiency drop at higher current densities, resulting in relatively low wall-plug efficiency. Multi-active region approach can improve the wall-plug efficiency significantly and tackle the green gap challenge. This work reports multi-active region p-down LEDs with high external efficiency operating entirely in the green wavelength…
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Longer wavelength emitters such as green LEDs display a pronounced efficiency drop at higher current densities, resulting in relatively low wall-plug efficiency. Multi-active region approach can improve the wall-plug efficiency significantly and tackle the green gap challenge. This work reports multi-active region p-down LEDs with high external efficiency operating entirely in the green wavelength. Devices were developed using p-down topology, where the PN junction is oriented such that electric fields from depletion and built-in polarization dipoles are aligned. Ga-polar multi-active region green LEDs with excellent voltage and EQE scaling, and significantly higher wall-plug efficiency is demonstrated in this work.
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Submitted 10 October, 2023; v1 submitted 10 August, 2023;
originally announced August 2023.
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Anisotropic excitonic photocurrent in $β$-Ga$_{2}$O$_{3}$
Authors:
Darpan Verma,
Md Mohsinur Rahman Adnan,
Sushovan Dhara,
Chris Sturm,
Siddharth Rajan,
Roberto C. Myers
Abstract:
Polarization dependent photocurrent spectra are measured on a (001) $β$-Ga$_{2}$O$_{3}$ Schottky photodetector, where the linear polarization of light is rotated within the ab plane. Three spectral peaks at 4.92 eV, 5.15 eV, and 5.44 eV are observed that vary in intensity with the optical polarization direction. The peak transition energies are consistent with excitons previously reported in $β$-G…
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Polarization dependent photocurrent spectra are measured on a (001) $β$-Ga$_{2}$O$_{3}$ Schottky photodetector, where the linear polarization of light is rotated within the ab plane. Three spectral peaks at 4.92 eV, 5.15 eV, and 5.44 eV are observed that vary in intensity with the optical polarization direction. The peak transition energies are consistent with excitons previously reported in $β$-Ga$_{2}$O$_{3}$ due to interband transitions modified by the valence band p-orbital anisotropy and the electron-hole Coulombic attraction. The measured polarization-dependence of the photocurrent matches our predictions based on electromagnetic simulations of anisotropic absorption using the complex dielectric function tensor extracted from previous ellipsometry studies. These results illustrate the dominance of excitonic absorption and photocurrent in $β$-Ga$_{2}$O$_{3}$ both below and above the band gap, demonstrate a combined theoretical/experimental understanding of anisotropic photocarrier generation, and validate previous atomistic band structure calculations in this low-symmetry ultra-wide band gap semiconductor.
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Submitted 10 March, 2023;
originally announced March 2023.
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$β$-Ga$_2$O$_3$ Trench Schottky Diodes by Novel Low-Damage Ga-Flux Etching
Authors:
Sushovan Dhara,
Nidhin Kurian Kalarickal,
Ashok Dheenan,
Sheikh Ifatur Rahman,
Chandan Joishi,
Siddharth Rajan
Abstract:
$β$-Ga$_2$O$_3…
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$β$-Ga$_2$O$_3$ trench Schottky barrier diodes fabricated through a Gallium atomic beam etching technique, with excellent field strength and power device figure of merit, are demonstrated. Trench formation was accomplished by a low-damage Ga flux etch that enables near-ideal forward operating characteristics that are independent of fin orientation. The reverse breakdown field strength of greater than 5.10 MV/cm is demonstrated at breakdown voltage as of 1.45 kV. This result demonstrates the potential for Ga atomic beam etching and high-quality dielectric layers for improved performance in $β$-Ga$_2$O$_3$ vertical power devices.
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Submitted 8 March, 2023;
originally announced March 2023.
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Simulation of GaN-Based Light Emitting Diodes Incorporating Composition Fluctuation Effects
Authors:
Sheikh Ifatur Rahman,
Zane Jamal-Eddine,
Zhanbo Xia,
Mohammad Awwad,
Rob Armitage,
Siddharth Rajan
Abstract:
III-Nitride light emitting diodes (LEDs) are widely used in a range of high efficiency lighting and display applications, which have enabled significant energy savings in the last decade. Despite the wide application of GaN LEDs, transport mechanisms across InGaN/GaN heterostructures in these devices are not well-explained. Fixed polarization sheet charges at InGaN/GaN interfaces lead to large int…
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III-Nitride light emitting diodes (LEDs) are widely used in a range of high efficiency lighting and display applications, which have enabled significant energy savings in the last decade. Despite the wide application of GaN LEDs, transport mechanisms across InGaN/GaN heterostructures in these devices are not well-explained. Fixed polarization sheet charges at InGaN/GaN interfaces lead to large interface dipole charges, which create large potential barriers to overcome. One-dimensional models for transport across such heterostructures predict turn-on voltages that are significantly higher than that found in real devices. As a result, conventional models for transport cannot predict the performance of new designs such as for longer wavelength LEDs, or for multi-quantum well LEDs. In this work, we show that incorporating low and high Indium compositions within quantum wells at the submicron scale can provide accurate prediction of the characteristics of GaN/InGaN light emitting diodes.
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Submitted 10 November, 2022;
originally announced November 2022.
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Planar and 3-dimensional damage free etching of $β$-Ga2O3 using atomic gallium flux
Authors:
Nidhin Kurian Kalarickal,
Andreas Fiedler,
Sushovan Dhara,
Mohammad Wahidur Rahman,
Taeyoung Kim,
Zhanbo Xia,
Zane Jamal Eddine,
Ashok Dheenan,
Mark Brenner,
Siddharth Rajan
Abstract:
In-situ etching using Ga flux in an ultra-high vacuum environment like MBE is introduced as a method to make high aspect ratio 3 dimensional structures in $β$-Ga2O3. Etching of $β$-Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of growth rate. In this study, we use this well-known react…
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In-situ etching using Ga flux in an ultra-high vacuum environment like MBE is introduced as a method to make high aspect ratio 3 dimensional structures in $β$-Ga2O3. Etching of $β$-Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of growth rate. In this study, we use this well-known reaction from epitaxial growth to intentionally etch $β$-Ga2O3. We demonstrate etch rate ranging from 2.9 nm/min to 30 nm/min with the highest reported etch rate being only limited by the highest Ga flux used. Patterned in-situ etching is also demonstrated and used to study the effect of fin orientation on the sidewall profiles and dopant (Si) segregation on the etched surface. Using in-situ Ga etching, we also demonstrate 150 nm wide fins and 200 nm wide nano pillars with high aspect ratio. This new etching method could enable future development of highly scaled vertical and lateral 3D devices in $β$-Ga2O3.
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Submitted 26 July, 2021; v1 submitted 20 May, 2021;
originally announced May 2021.
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Electrostatic Engineering using Extreme Permittivity Materials for Ultra-wide Bandgap Semiconductor Transistors
Authors:
Nidhin Kurian Kalarickal,
Zixuan Feng,
A F M Anhar Uddin Bhuiyan,
Zhanbo Xia,
Joe F. McGlone,
Wyatt Moore,
Aaron R. Arehart,
Steven A. Ringel,
Hongping Zhao,
Siddharth Rajan
Abstract:
The performance of ultra-wide band gap materials like $β$-Ga$_\mathrm{2}$O$_\mathrm{3}$ is critically dependent on achieving high average electric fields within the active region of the device. In this report, we show that high-k gate dielectrics like BaTiO$_\mathrm{3}$ can provide an efficient field management strategy by improving the uniformity of electric field profile in the gate-drain region…
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The performance of ultra-wide band gap materials like $β$-Ga$_\mathrm{2}$O$_\mathrm{3}$ is critically dependent on achieving high average electric fields within the active region of the device. In this report, we show that high-k gate dielectrics like BaTiO$_\mathrm{3}$ can provide an efficient field management strategy by improving the uniformity of electric field profile in the gate-drain region of lateral field effect transistors. Using this strategy, we were able to achieve high average breakdown fields of 1.5 MV/cm and 4 MV/cm at gate-drain spacing (L$_\mathrm{gd}$) of 6 um and 0.6 um respectively in $β$-Ga$_\mathrm{2}$O$_\mathrm{3}$, at a high channel sheet charge density of 1.8x10$^\mathrm{13}$cm$^\mathrm{-2}$. The high sheet charge density together with high breakdown field enabled a record power figure of merit (V$^\mathrm{2}$$_\mathrm{br}$/R$_\mathrm{on}$) of 376 MW/cm$^\mathrm{2}$ at a gate-drain spacing of 3 um.
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Submitted 3 June, 2020;
originally announced June 2020.
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Probing charge transport and background doping in MOCVD grown (010) $β$-Ga$_{2}$O$_{3}$
Authors:
Zixuan Feng,
A F M Anhar Uddin Bhuiyan,
Zhanbo Xia,
Wyatt Moore,
Zhaoying Chen,
Joe F. McGlone,
David R. Daughton,
Aaron R. Arehart,
Steven A. Ringel,
Siddharth Rajan,
Hongping Zhao
Abstract:
A new record-high room temperature electron Hall mobility ($μ_{RT} = 194\space cm^{2}/V\space s$ at $n\sim 8\times 10^{15}\space cm^{-3}$) for $β$-Ga2O3 is demonstrated in the unintentionally doped thin film grown on (010) semi-insulating substrate via metalorganic chemical vapor deposition (MOCVD). A peak electron mobility of $\sim 9500\space cm^{2}/V\space s$ is achieved at 45 K. Further investi…
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A new record-high room temperature electron Hall mobility ($μ_{RT} = 194\space cm^{2}/V\space s$ at $n\sim 8\times 10^{15}\space cm^{-3}$) for $β$-Ga2O3 is demonstrated in the unintentionally doped thin film grown on (010) semi-insulating substrate via metalorganic chemical vapor deposition (MOCVD). A peak electron mobility of $\sim 9500\space cm^{2}/V\space s$ is achieved at 45 K. Further investigation on the transport properties indicate the existence of sheet charges near the epi-layer/substrate interface. Si is identified as the primary contributor to the background carrier in both the epi-layer and the interface, originated from both surface contamination as well as growth environment. Pre-growth hydrofluoric acid cleaning of the substrate lead to an obvious decrease of Si impurity both at interface and in epi-layer. In addition, the effect of MOCVD growth condition, particularly the chamber pressure, on the Si impurity incorporation is studied. A positive correlation between the background charge concentration and the MOCVD growth pressure is confirmed. It is noteworthy that in a $β$-Ga2O3 film with very low bulk charge concentration, even a reduced sheet charge density can play an important role in the charge transport properties.
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Submitted 27 April, 2020;
originally announced April 2020.
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Deep-recessed $β$-Ga$_2$O$_3$ delta-doped field effect transistors with in situ epitaxial passivation
Authors:
Chandan Joishi,
Zhanbo Xia,
John S. Jamison,
Shahadat H. Sohel,
Roberto C. Myers,
Saurabh Lodha,
Siddharth Rajan
Abstract:
We introduce a deep-recessed gate architecture in $β$-Ga$_2$O$_3$ delta-doped field effect transistors for improvement in DC-RF dispersion and breakdown properties. The device design incorporates an unintentionally doped $β$-Ga$_2$O$_3$ layer as the passivation dielectric. To fabricate the device, the deep-recess geometry was developed using BCl$_3$ plasma based etching at ~5 W RIE to ensure minim…
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We introduce a deep-recessed gate architecture in $β$-Ga$_2$O$_3$ delta-doped field effect transistors for improvement in DC-RF dispersion and breakdown properties. The device design incorporates an unintentionally doped $β$-Ga$_2$O$_3$ layer as the passivation dielectric. To fabricate the device, the deep-recess geometry was developed using BCl$_3$ plasma based etching at ~5 W RIE to ensure minimal plasma damage. Etch damage incurred with plasma etching was mitigated by annealing in vacuum at temperatures above 600 $°$C. A gate-connected field-plate edge termination was implemented for efficient field management. Negligible surface dispersion with lower knee-walkout at high V$_\mathrm{DS}$, and better breakdown characteristics compared to their unpassivated counterparts were achieved. A three terminal off-state breakdown voltage of 315 V, corresponding to an average breakdown field of 2.3 MV/cm was measured. The device breakdown was limited by the field-plate/passivation edge and presents scope for further improvement. This demonstration of epitaxially passivated field effect transistors is a significant step for $β$-Ga$_2$O$_3$ technology since the structure simultaneously provides control of surface-related dispersion and excellent field management.
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Submitted 22 April, 2020;
originally announced April 2020.
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Local Electric Field Measurement in GaN Diodes by exciton Franz-Keldysh Photocurrent Spectroscopy
Authors:
Darpan Verma,
Md Mohsinur Rahman Adnan,
Mohammad Wahidur Rahman,
Siddharth Rajan,
Roberto C. Myers
Abstract:
The eXciton Franz-Keldysh (XFK) effect is observed in GaN p-n junction diodes via the spectral variation of photocurrent responsivity data that redshift and broaden with increasing reverse bias. Photocurrent spectra are quantitatively fit over a broad photon energy range to an XFK model using only a single fit parameter that determines the lineshape, the local bias ($V_{l}$), uniquely determining…
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The eXciton Franz-Keldysh (XFK) effect is observed in GaN p-n junction diodes via the spectral variation of photocurrent responsivity data that redshift and broaden with increasing reverse bias. Photocurrent spectra are quantitatively fit over a broad photon energy range to an XFK model using only a single fit parameter that determines the lineshape, the local bias ($V_{l}$), uniquely determining the local electric field maximum and depletion widths. As expected, the spectrally determined values of $V_{l}$ vary linearly with the applied bias ($V$) and reveal a large reduction in the local electric field due to electrostatic non-uniformity. The built-in bias ($V_{bi}$) is estimated by extrapolating $V_{l}$ at $V=0$, which compared with independent C-V measurements indicates an overall $\pm$0.31 V accuracy of $V_{l}$. This demonstrates sub-bandgap photocurrent spectroscopy as a local probe of electric field in wide bandgap diodes that can be used to map out regions of device breakdown (hot spots) for improving electrostatic design of high voltage devices.
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Submitted 1 April, 2020; v1 submitted 10 January, 2020;
originally announced January 2020.
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Metal$/BaTiO_{3}/β-Ga_{2}O_{3}$ Dielectric Heterojunction Diode with 5.7 MV/cm Breakdown Field
Authors:
Zhanbo Xia,
Hareesh Chandrasekar,
Wyatt Moore,
Caiyu Wang,
Aidan Lee,
Joe McGlone,
Nidhin Kurian Kalarickal,
Aaron Arehart,
Steven Ringel,
Fengyuan Yang,
Siddharth Rajan
Abstract:
Wide and ultra-wide band gap semiconductors can provide excellent performance due to their high energy band gap, which leads to breakdown electric fields that are more than an order of magnitude higher than conventional silicon electronics. In materials where p-type doping is not available, achieving this high breakdown field in a vertical diode or transistor is very challenging. We propose and de…
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Wide and ultra-wide band gap semiconductors can provide excellent performance due to their high energy band gap, which leads to breakdown electric fields that are more than an order of magnitude higher than conventional silicon electronics. In materials where p-type doping is not available, achieving this high breakdown field in a vertical diode or transistor is very challenging. We propose and demonstrate the use of dielectric heterojunctions that use extreme permittivity materials to achieve high breakdown field in a unipolar device. We demonstrate the integration of a high permittivity material BaTiO3 with n-type $β$-Ga2O3 to enable 5.7 MV/cm average electric field and 7 MV/cm peak electric field at the device edge, while maintaining forward conduction with relatively low on-resistance and voltage loss. The proposed dielectric heterojunction could enable new design strategies to achieve theoretical device performance limits in wide and ultra-wide band gap semiconductors where bipolar doping is challenging.
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Submitted 5 November, 2019;
originally announced November 2019.
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High electron density $β-(Al_{0.18}Ga_{0.82})_2O_3/Ga_2O_3$ modulation doping using ultra-thin (1 nm) spacer layer
Authors:
Nidhin Kurian Kalarickal,
Zhanbo Xia,
Joe Mcglone,
Yumo Liu,
Wyatt Moore,
Aaron Arehart,
Steve Ringel,
Siddharth Rajan
Abstract:
We report on the design and demonstration of $β-(Al_{0.18}Ga_{0.82})_2O_3/Ga_2O_3$ modulation doped heterostructures to achieve high sheet charge density. The use of a thin spacer layer between the Si delta-doping and heterojunction interface was investigated in $β-(Al_{0.18}Ga_{0.82})_2O_3/Ga_2O_3$ modulation doped structures. We find that that this strategy enables higher 2DEG sheet charge densi…
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We report on the design and demonstration of $β-(Al_{0.18}Ga_{0.82})_2O_3/Ga_2O_3$ modulation doped heterostructures to achieve high sheet charge density. The use of a thin spacer layer between the Si delta-doping and heterojunction interface was investigated in $β-(Al_{0.18}Ga_{0.82})_2O_3/Ga_2O_3$ modulation doped structures. We find that that this strategy enables higher 2DEG sheet charge density up to 6.1x10^12 cm^2 with mobility of 147 cm^2/Vs. The presence of a degenerate 2DEG channel was confirmed by the measurement of low temperature effective mobility of 378 cm^2/V-s and a lack of carrier freeze out from low temperature capacitance voltage measurements. The electron density of 6.1x10^12 cm^2 is the highest reported sheet charge density obtained without parallel conduction channels in an $(Al_{0.18}Ga_{0.82})_2O_3/Ga_2O_3$ heterostructure system.
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Submitted 25 October, 2019;
originally announced October 2019.
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Lateral Heterojunction BaTiO3/AlGaN Diodes with >8MV/cm Breakdown Field
Authors:
Towhidur Razzak,
Hareesh Chandrasekar,
Kamal Hussain,
Choong Hee Lee,
Abdullah Mamun,
Hao Xue,
Zhanbo Xia,
Shahadat H. Sohel,
Mohammad Wahidur Rahman,
Sanyam Bajaj,
Caiyu Wang,
Wu Lu,
Asif Khan,
Siddharth Rajan
Abstract:
In this paper, we report enhanced breakdown characteristics of Pt/BaTiO3/Al0.58Ga0.42N lateral heterojunction diodes compared to Pt/Al0.58Ga0.42N Schottky diodes. BaTiO3, an extreme dielectric constant material, has been used, in this study, as dielectric material under the anode to significantly reduce the peak electric field at the anode edge of the heterojunction diode such that the observed av…
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In this paper, we report enhanced breakdown characteristics of Pt/BaTiO3/Al0.58Ga0.42N lateral heterojunction diodes compared to Pt/Al0.58Ga0.42N Schottky diodes. BaTiO3, an extreme dielectric constant material, has been used, in this study, as dielectric material under the anode to significantly reduce the peak electric field at the anode edge of the heterojunction diode such that the observed average breakdown field was higher than 8 MV/cm, achieved for devices with anode to cathode spacing less than 0.2 microns. Control Schottky anode devices (Pt/Al0.58Ga0.42N) fabricated on the same sample displayed an average breakdown field around 4 MV/cm for devices with similar dimensions. While both breakdown fields are significantly higher than those exhibited by incumbent technologies such as GaN-based devices, BaTiO3 can enable more effective utilization of the higher breakdown fields available in ultra-wide bandgap materials by proper electric field management. This demonstration thus lays the groundwork needed to realize ultra-scaled lateral devices with significantly improved breakdown characteristics.
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Submitted 5 October, 2019;
originally announced October 2019.
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Mechanism of Si doping in Plasma Assisted MBE Growth of \b{eta}-Ga2O3
Authors:
Nidhin Kurian Kalarickal,
Zhanbo Xia,
Joe McGlone,
Sriram Krishnamoorthy,
Wyatt Moore,
Mark Brenner,
Aaron R. Arehart,
Steven A. Ringel,
Siddharth Rajan
Abstract:
We report on the origin of high Si flux observed during the use of Si as a doping source in plasma assisted MBE growth of \b{eta}-Ga2O3. We show on the basis of secondary ion mass spectroscopy (SIMS) analysis that Si flux is not limited by the vapor pressure of Si but by the formation of volatile SiO. The low sublimation energy of SiO leads to weak dependence of the SiO flux of Si cell temperature…
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We report on the origin of high Si flux observed during the use of Si as a doping source in plasma assisted MBE growth of \b{eta}-Ga2O3. We show on the basis of secondary ion mass spectroscopy (SIMS) analysis that Si flux is not limited by the vapor pressure of Si but by the formation of volatile SiO. The low sublimation energy of SiO leads to weak dependence of the SiO flux of Si cell temperature and a strong dependence on the background oxygen pressure. Extended exposure to activated oxygen results in reduction of SiO flux due to the formation of SiO2 on the Si surface. The work reported provides key understanding for incorporating Si into future oxide-based semiconductor heterostructure and device MBE growth.
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Submitted 2 August, 2019;
originally announced August 2019.
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Compositionally graded contact layers for MOCVD grown high Al-content AlGaN transistors
Authors:
Towhidur Razzak,
Seongmo Hwang,
Antwon Coleman,
Hao Xue,
Shahadat Hasan Sohel,
Sanyam Bajaj,
Yuewei Zhang,
Wu Lu,
Asif Khan,
Siddharth Rajan
Abstract:
In this letter, we design and demonstrate an improved MOCVD grown reverse Al-composition graded contact layer to achieve low resistance contact to MOCVD grown ultra-wide bandgap (UWBG) Al0.70Ga0.30N channel metal semiconductor field-effect transistors (MESFETs). Increasing the thickness of the reverse graded layer was found to improve contact layer resistance significantly, leading to contact resi…
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In this letter, we design and demonstrate an improved MOCVD grown reverse Al-composition graded contact layer to achieve low resistance contact to MOCVD grown ultra-wide bandgap (UWBG) Al0.70Ga0.30N channel metal semiconductor field-effect transistors (MESFETs). Increasing the thickness of the reverse graded layer was found to improve contact layer resistance significantly, leading to contact resistance of 3.3x10^-5 Ohm.cm2. Devices with gate length, LG, of 0.6 microns and source-drain spacing, LSD, of 1.5 microns displayed a maximum current density, IDSMAX, of 635 mA/mm with an applied gate voltage, VGS, of +2 V. Breakdown measurements on transistors with gate to drain spacing, LGD, of 770 nm had breakdown voltage greater than 220 , corresponding to minimum breakdown field of 2.86 MV/cm. This work provides a framework for the design of low resistance contacts to MOCVD grown high Al-content AlxGa1-xN channel transistors.
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Submitted 15 September, 2019; v1 submitted 24 June, 2019;
originally announced June 2019.
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Velocity Saturation in La-doped BaSnO3 Thin Films
Authors:
Hareesh Chandrasekar,
Junao Cheng,
Tianshi Wang,
Zhanbo Xia,
Nicholas G. Combs,
Christopher R. Freeze,
Patrick B. Marshall,
Joe McGlone,
Aaron Arehart,
Steven Ringel,
Anderson Janotti,
Susanne Stemmer,
Wu Lu,
Siddharth Rajan
Abstract:
BaSnO_{3}, a high mobility perovskite oxide, is an attractive material for oxide-based electronic devices. However, in addition to low-field mobility, high-field transport properties such as the saturation velocity of carriers play a major role in determining device performance. We report on the experimental measurement of electron saturation velocity in La-doped BaSnO_{3} thin films for a range o…
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BaSnO_{3}, a high mobility perovskite oxide, is an attractive material for oxide-based electronic devices. However, in addition to low-field mobility, high-field transport properties such as the saturation velocity of carriers play a major role in determining device performance. We report on the experimental measurement of electron saturation velocity in La-doped BaSnO_{3} thin films for a range of doping densities. Predicted saturation velocities based on a simple LO-phonon emission model using an effective LO phonon energy of 120 meV show good agreement with measurements of velocity saturation in La-doped BaSnO_{3} films.. Density-dependent saturation velocity in the range of 1.6x10^{7} cm/s reducing to 2x10^{6} cm/s is predicted for δ-doped BaSnO3 channels with carrier densities ranging from 10^{13} cm^{-2} to 2x10^{14} cm^{-2} respectively. These results are expected to aid the informed design of BaSnO3 as the active material for high-charge density electronic transistors.
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Submitted 3 August, 2019; v1 submitted 13 May, 2019;
originally announced May 2019.
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MBE grown Self-Powered \b{eta}-Ga2O3 MSM Deep-UV Photodetector
Authors:
Anamika Singh Pratiyush,
Sriram Krishnamoorthy,
Sandeep Kumar,
Zhanbo Xia,
Rangarajan Muralidharan,
Siddharth Rajan,
Digbijoy N. Nath
Abstract:
We demonstrate self-powered \b{eta}-Ga2O3 deep-UV metal-semiconductor-metal (MSM) photodetectors (PD) with 0.5% external quantum efficiency (EQE) at zero bias. 150 nm thick (-201)-oriented epitaxial \b{eta}-Ga2O3-films were grown on c-plane sapphire using plasma-assisted MBE. Ni/Au and Ti/Au metal stacks were deposited as contacts to achieve asymmetric Schottky barrier heights in interdigitated fi…
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We demonstrate self-powered \b{eta}-Ga2O3 deep-UV metal-semiconductor-metal (MSM) photodetectors (PD) with 0.5% external quantum efficiency (EQE) at zero bias. 150 nm thick (-201)-oriented epitaxial \b{eta}-Ga2O3-films were grown on c-plane sapphire using plasma-assisted MBE. Ni/Au and Ti/Au metal stacks were deposited as contacts to achieve asymmetric Schottky barrier heights in interdigitated finger architecture for realizing self-powered photodetectors. Current-voltage characteristics (photo and dark), time-dependent photocurrent and spectral response were studied and compared with conventional symmetric MSM PD with Ni/Au as the Schottky metal contact, fabricated on the same sample. The asymmetric, self-powered devices exhibited solar-blind nature and low dark current < 10 nA at 15 V with high photo-to-dark current ratio of ~ 103. The dark and photocurrents were asymmetric with respect to the applied bias and the responsivity in the forward bias was characterized by gain. The detectors (asymmetric-MSM) were found to exhibit a responsivity of 1.4 mA/W at 255 nm under zero-bias condition (corresponding to an EQE ~ 0.5 %), with a UV-to-Visible rejection ratio ~ 102 and ~105 at 0 V and 5 V respectively.
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Submitted 5 February, 2018;
originally announced February 2018.
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Modulation-doped beta-(Al0.2Ga0.8)2O3/Ga2O3 Field-Effect Transistor
Authors:
Sriram Krishnamoorthy,
Zhanbo Xia,
Chandan Joishi,
Yuewei Zhang,
Joe McGlone,
Jared Johnson,
Mark Brenner,
Aaron R. Arehart,
Jinwoo Hwang,
Saurabh Lodha,
Siddharth Rajan
Abstract:
Modulation-doped heterostructures are a key enabler for realizing high mobility and better scaling properties for high performance transistors. We report the realization of modulation-doped two-dimensional electron gas (2DEG) at beta(Al0.2Ga0.8)2O3/ Ga2O3 heterojunction using silicon delta doping. The formation of a 2DEG was confirmed using capacitance voltage measurements. A modulation-doped 2DEG…
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Modulation-doped heterostructures are a key enabler for realizing high mobility and better scaling properties for high performance transistors. We report the realization of modulation-doped two-dimensional electron gas (2DEG) at beta(Al0.2Ga0.8)2O3/ Ga2O3 heterojunction using silicon delta doping. The formation of a 2DEG was confirmed using capacitance voltage measurements. A modulation-doped 2DEG channel was used to realize a modulation-doped field-effect transistor. The demonstration of modulation doping in the beta-(Al0.2Ga0.8)2O3/ Ga2O3 material system could enable heterojunction devices for high performance electronics.
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Submitted 28 June, 2017;
originally announced June 2017.
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Reflective Metal/Semiconductor Tunnel Junctions for Hole Injection in AlGaN UV LEDs
Authors:
Yuewei Zhang,
Sriram Krishnamoorthy,
Fatih Akyol,
Jared M. Johnson,
Andrew A. Allerman,
Michael W. Moseley,
Andrew M. Armstrong,
Jinwoo Hwang,
Siddharth Rajan
Abstract:
In this work, we investigate the use of nanoscale polarization engineering to achieve efficient hole injection from metals to ultra-wide band gap AlGaN, and we show that UV-reflective aluminum (Al) layers can be used for hole injection into p-AlGaN. The dependence of tunneling on the work function of the metal was investigated, and it was found that highly reflective Al metal layers can enable eff…
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In this work, we investigate the use of nanoscale polarization engineering to achieve efficient hole injection from metals to ultra-wide band gap AlGaN, and we show that UV-reflective aluminum (Al) layers can be used for hole injection into p-AlGaN. The dependence of tunneling on the work function of the metal was investigated, and it was found that highly reflective Al metal layers can enable efficient hole injection into p-AlGaN, despite the relatively low work function of Al. Efficient tunneling hole injection was confirmed by light emission at 326 nm with on-wafer peak external quantum efficiency and wall-plug efficiency of 2.65% and 1.55%, respectively. A high power density of 83.7 W/cm2 was measured at 1200 kA/cm2. The metal/semiconductor tunnel junction structure demonstrated here could provide significant advantages for efficient and manufacturable device topologies for high power UV emitters.
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Submitted 19 May, 2017;
originally announced May 2017.
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Delta-doped Beta- Gallium Oxide Field Effect Transistor
Authors:
Sriram Krishnamoorthy,
Zhanbo Xia,
Sanyam Bajaj,
Mark Brenner,
Siddharth Rajan
Abstract:
We report silicon delta doping in Gallium Oxide (\b{eta}-Ga2O3) grown by plasma assisted molecular beam epitaxy using a shutter pulsing technique. We describe growth procedures that can be used to realize high Si incorporation in an oxidizing oxygen plasma environment. Delta doping was used to realize thin (12 nm) low-resistance layers with sheet resistance of 320 Ohm/square (mobility of 83 cm^2/V…
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We report silicon delta doping in Gallium Oxide (\b{eta}-Ga2O3) grown by plasma assisted molecular beam epitaxy using a shutter pulsing technique. We describe growth procedures that can be used to realize high Si incorporation in an oxidizing oxygen plasma environment. Delta doping was used to realize thin (12 nm) low-resistance layers with sheet resistance of 320 Ohm/square (mobility of 83 cm^2/Vs, integrated sheet charge of 2.4x10^14 cm^-2). A single delta-doped sheet of carriers was employed as a channel to realize a field effect transistor with current ID,MAX =292 mA/mm and transconductance gM = 27 mS/mm.
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Submitted 18 February, 2017;
originally announced February 2017.
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Design of P-Type Cladding Layers for Tunnel-Injected UVA Light Emitting Diodes
Authors:
Yuewei Zhang,
Sriram Krishnamoorthy,
Fatih Akyol,
Andrew A. Allerman,
Michael W. Moseley,
Andrew M. Armstrong,
Siddharth Rajan
Abstract:
We discuss the engineering of p-AlGaN cladding layers for achieving efficient tunnel-injected III-Nitride ultraviolet light emitting diodes (UV LEDs) in the UV-A spectral range. We show that capacitance-voltage measurements can be used to estimate the compensation and doping in p-AlGaN layers located between the multi-quantum well region and the tunnel junction layer. By increasing the p-type dopi…
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We discuss the engineering of p-AlGaN cladding layers for achieving efficient tunnel-injected III-Nitride ultraviolet light emitting diodes (UV LEDs) in the UV-A spectral range. We show that capacitance-voltage measurements can be used to estimate the compensation and doping in p-AlGaN layers located between the multi-quantum well region and the tunnel junction layer. By increasing the p-type doping concentration to overcome the background compensation, on-wafer external quantum efficiency and wall-plug efficiency of 3.37% and 1.62% were achieved for tunnel-injected UV LEDs emitting at 325 nm. We also show that interband tunneling hole injection can be used to realize UV LEDs without any acceptor doping. The work discussed here provides new understanding of hole doping and transport in AlGaN-based UV LEDs, and demonstrates the excellent performance of tunnel-injected LEDs for the UV-A wavelength range.
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Submitted 17 August, 2016;
originally announced September 2016.
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High Current Density 2D/3D Esaki Tunnel Diodes
Authors:
Sriram Krishnamoorthy,
Edwin W. Lee II,
Choong Hee Lee,
Yuewei Zhang,
William D. McCulloch,
Jared M. Johnson,
Jinwoo Hwang,
Yiying Wu,
Siddharth Rajan
Abstract:
The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based novel device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area, Nb-dop…
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The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based novel device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area, Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current density of 446 A/cm2 with repeatable room temperature negative differential resistance, peak to valley current ratio of 1.2, and minimal hysteresis was measured in the MoS2/GaN non-epitaxial tunnel diode. A high current density of 1 kA/cm2 was measured in the Zener mode (reverse bias) at -1 V bias. The GaN/MoS2 tunnel junction was also modeled by treating MoS2 as a bulk semiconductor, and the electrostatics at the 2D/3D interface was found to be crucial in explaining the experimentally observed device characteristics.
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Submitted 1 June, 2016;
originally announced June 2016.
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Simulation of Enhancement Mode GaN HEMTs with Threshold > 5 V using P-type Buffer
Authors:
Sanyam Bajaj,
Fatih Akyol,
Sriram Krishnamoorthy,
Ting-Hsiang Hung,
Siddharth Rajan
Abstract:
A high threshold voltage enhancement-mode GaN HEMT with p-type doped buffer is discussed and simulated. Analytical expressions are derived to explain the role of buffer capacitance in designing and enhancing threshold voltage. Simulations of the proposed device with p-type buffer show threshold voltages above 5 V, and a positive shift in threshold voltage as the oxide capacitance is reduced, thus…
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A high threshold voltage enhancement-mode GaN HEMT with p-type doped buffer is discussed and simulated. Analytical expressions are derived to explain the role of buffer capacitance in designing and enhancing threshold voltage. Simulations of the proposed device with p-type buffer show threshold voltages above 5 V, and a positive shift in threshold voltage as the oxide capacitance is reduced, thus enabling threshold voltage tunability over an unprecedented range for GaN-based HEMTs. The electric field profiles, breakdown performance, on-resistance and delay tradeoffs in the proposed pGaN back HEMT device are also discussed.
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Submitted 12 November, 2015;
originally announced November 2015.
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Generalization of the Atkinson-Wilcox Theorem and the Development of a Novel Scaled Boundary Finite Element Formulation for the Numerical Simulation of Electromagnetic Radiation
Authors:
V. S. Prasanna Rajan
Abstract:
The Scaled Boundary Finite Element Method is a novel semi-analytical method jointly developed by Chongmin Song and John P Wolf to solve problems in elastodynamics and allied problems in civil engineering. This novel method has been recently reformulated for the following categories of problems in electromagnetics: (1) Determination of Eigen values of metallic cavity structures, 2) Full wave anal…
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The Scaled Boundary Finite Element Method is a novel semi-analytical method jointly developed by Chongmin Song and John P Wolf to solve problems in elastodynamics and allied problems in civil engineering. This novel method has been recently reformulated for the following categories of problems in electromagnetics: (1) Determination of Eigen values of metallic cavity structures, 2) Full wave analysis of Shielded micro-strip transmission line structures, and Very Large Scale Integrated Circuit (VLSI) interconnects, and 3) Full wave analysis of periodic structures. In this paper, a novel Scaled Boundary Finite Element formulation is developed for the numerical simulation of the time harmonic electromagnetic radiation in free space from metallic structures of arbitrary shape. The development of the novel formulation necessitates the generalization of the familiar Atkinson-Wilcox radiation series expansion so as to be applicable for arbitrary boundary circumscribing the source of radiation.
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Submitted 1 June, 2006; v1 submitted 19 March, 2006;
originally announced March 2006.
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Application of the Covariant projection finite elements in the E field formulation for wave guide analysis
Authors:
V. S. Prasanna Rajan,
K. C. James Raju
Abstract:
The use of covariant projection finite elements in the efficient 3-D vector finite element analysis of wave guide is presented.
The use of covariant projection finite elements in the efficient 3-D vector finite element analysis of wave guide is presented.
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Submitted 19 October, 2002;
originally announced October 2002.
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Divergence Condition for the novel Scaled Boundary Finite Element Method in Computational Electromagnetics
Authors:
V. S. Prasanna Rajan,
K. C. James Raju
Abstract:
The divergence condition is reformulated in the scaled boundary coordinates so as to prevent the spurious solutions in the finite element formulation.
The divergence condition is reformulated in the scaled boundary coordinates so as to prevent the spurious solutions in the finite element formulation.
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Submitted 19 October, 2002;
originally announced October 2002.
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A Novel Scaled Boundary Finite Element Method in Computational Electromagnetics
Authors:
V. S. Prasanna Rajan,
K. C. James Raju
Abstract:
A Novel Scaled boundary finite element method, initially developed in Civil Engineering, is reformulated for solving boundary value problems in computational electromagnetics.
A Novel Scaled boundary finite element method, initially developed in Civil Engineering, is reformulated for solving boundary value problems in computational electromagnetics.
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Submitted 19 October, 2002;
originally announced October 2002.