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Resistive Switching and Current Conduction Mechanisms in Hexagonal Boron Nitride Threshold Memristors with Nickel Electrodes
Authors:
Lukas Völkel,
Dennis Braun,
Melkamu Belete,
Satender Kataria,
Thorsten Wahlbrink,
Ke Ran,
Kevin Kistermann,
Joachim Mayer,
Stephan Menzel,
Alwin Daus,
Max C. Lemme
Abstract:
The two-dimensional (2D) insulating material hexagonal boron nitride (h BN) has attracted much attention as the active medium in memristive devices due to its favorable physical properties, among others, a wide bandgap that enables a large switching window. Metal filament formation is frequently suggested for h-BN devices as the resistive switching (RS) mechanism, usually supported by highly speci…
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The two-dimensional (2D) insulating material hexagonal boron nitride (h BN) has attracted much attention as the active medium in memristive devices due to its favorable physical properties, among others, a wide bandgap that enables a large switching window. Metal filament formation is frequently suggested for h-BN devices as the resistive switching (RS) mechanism, usually supported by highly specialized methods like conductive atomic force microscopy (C-AFM) or transmission electron microscopy (TEM). Here, we investigate the switching of multilayer hexagonal boron nitride (h-BN) threshold memristors with two nickel (Ni) electrodes through their current conduction mechanisms. Both the high and the low resistance states are analyzed through temperature-dependent current-voltage measurements. We propose the formation and retraction of nickel filaments along boron defects in the h-BN film as the resistive switching mechanism. We corroborate our electrical data with TEM analyses to establish temperature-dependent current-voltage measurements as a valuable tool for the analysis of resistive switching phenomena in memristors made of 2D materials. Our memristors exhibit a wide and tunable current operation range and low stand-by currents, in line with the state of the art in h-BN-based threshold switches, a low cycle-to-cycle variability of 5%, and a large On/Off ratio of 10${^7}$.
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Submitted 11 March, 2023; v1 submitted 11 January, 2023;
originally announced January 2023.
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Enhanced intrinsic voltage gain in artificially stacked bilayer CVD graphene field effect transistors
Authors:
Himadri Pandey,
Jorge Daniel Aguirre Morales,
Satender Kataria,
Sebastien Fregonese,
Vikram Passi,
Mario Iannazzo,
Thomas Zimmer,
Eduard Alarcon,
Max C. Lemme
Abstract:
We report on electronic transport in dual-gate, artificially stacked bilayer graphene field effect transistors (BiGFETs) fabricated from large-area chemical vapor deposited (CVD) graphene. The devices show enhanced tendency to current saturation, which leads to reduced minimum output conductance values. This results in improved intrinsic voltage gain of the devices when compared to monolayer graph…
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We report on electronic transport in dual-gate, artificially stacked bilayer graphene field effect transistors (BiGFETs) fabricated from large-area chemical vapor deposited (CVD) graphene. The devices show enhanced tendency to current saturation, which leads to reduced minimum output conductance values. This results in improved intrinsic voltage gain of the devices when compared to monolayer graphene FETs. We employ a physics based compact model originally developed for Bernal stacked bilayer graphene FETs (BSBGFETs) to explore the observed phenomenon. The improvement in current saturation may be attributed to increased charge carrier density in the channel and thus reduced saturation velocity due to carrier-carrier scattering.
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Submitted 4 December, 2022;
originally announced December 2022.
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Contact Resistance Study of Various Metal Electrodes with CVD Graphene
Authors:
Amit Gahoi,
Stefan Wagner,
Andreas Bablich,
Satender Kataria,
Vikram Passi,
Max C. Lemme
Abstract:
In this study, the contact resistance of various metals to chemical vapour deposited (CVD) monolayer graphene is investigated. Transfer length method (TLM) structures with varying widths and separation between contacts have been fabricated and electrically characterized in ambient air and vacuum condition. Electrical contacts are made with five metals: gold, nickel, nickel/gold, palladium and plat…
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In this study, the contact resistance of various metals to chemical vapour deposited (CVD) monolayer graphene is investigated. Transfer length method (TLM) structures with varying widths and separation between contacts have been fabricated and electrically characterized in ambient air and vacuum condition. Electrical contacts are made with five metals: gold, nickel, nickel/gold, palladium and platinum/gold. The lowest value of 92 Ωμm is observed for the contact resistance between graphene and gold, extracted from back-gated devices at an applied back-gate bias of -40 V. Measurements carried out under vacuum show larger contact resistance values when compared with measurements carried out in ambient conditions. Post processing annealing at 450°C for 1 hour in argon-95% / hydrogen-5% atmosphere results in lowering the contact resistance value which is attributed to the enhancement of the adhesion between metal and graphene. The results presented in this work provide an overview for potential contact engineering for high performance graphene-based electronic devices.
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Submitted 22 November, 2022;
originally announced November 2022.
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Correlating Nanocrystalline Structure with Electronic Properties in 2D Platinum Diselenide
Authors:
Sebastian Lukas,
Oliver Hartwig,
Maximilian Prechtl,
Giovanna Capraro,
Jens Bolten,
Alexander Meledin,
Joachim Mayer,
Daniel Neumaier,
Satender Kataria,
Georg S. Duesberg,
Max C. Lemme
Abstract:
Platinum diselenide (PtSe${_2}$) is a two-dimensional (2D) material with outstanding electronic and piezoresistive properties. The material can be grown at low temperatures in a scalable manner which makes it extremely appealing for many potential electronics, photonics, and sensing applications. Here, we investigate the nanocrystalline structure of different PtSe${_2}$ thin films grown by thermal…
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Platinum diselenide (PtSe${_2}$) is a two-dimensional (2D) material with outstanding electronic and piezoresistive properties. The material can be grown at low temperatures in a scalable manner which makes it extremely appealing for many potential electronics, photonics, and sensing applications. Here, we investigate the nanocrystalline structure of different PtSe${_2}$ thin films grown by thermally assisted conversion (TAC) and correlate them with their electronic and piezoresistive properties. We use scanning transmission electron microscopy for structural analysis, X-ray photoelectron spectroscopy (XPS) for chemical analysis, and Raman spectroscopy for phase identification. Electronic devices are fabricated using transferred PtSe${_2}$ films for electrical characterization and piezoresistive gauge factor measurements. The variations of crystallite size and their orientations are found to have a strong correlation with the electronic and piezoresistive properties of the films, especially the sheet resistivity and the effective charge carrier mobility. Our findings may pave the way for tuning and optimizing the properties of TAC-grown PtSe${_2}$ towards numerous applications.
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Submitted 8 April, 2021;
originally announced April 2021.
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Chemical vapor deposited graphene: From synthesis to applications
Authors:
Satender Kataria,
Stefan Wagner,
Jasper Ruhkopf,
Aamit Gahoi,
Himadri Pandey,
Rainer Bornemann,
Sam Vaziri,
Anderson D. Smith,
Mikael Östling,
Max C. Lemme
Abstract:
Graphene is a material with enormous potential for numerous applications. Therefore, significant efforts are dedicated to large-scale graphene production using a chemical vapor deposition (CVD) technique. In addition, research is directed at developing methods to incorporate graphene in established production technologies and process flows. In this paper, we present a brief review of available CVD…
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Graphene is a material with enormous potential for numerous applications. Therefore, significant efforts are dedicated to large-scale graphene production using a chemical vapor deposition (CVD) technique. In addition, research is directed at developing methods to incorporate graphene in established production technologies and process flows. In this paper, we present a brief review of available CVD methods for graphene synthesis. We also discuss scalable methods to transfer graphene onto desired substrates. Finally, we discuss potential applications that would benefit from a fully scaled, semiconductor technology compatible production process.
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Submitted 27 March, 2021;
originally announced March 2021.
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Capacitance-Voltage (C-V) Characterization of Graphene-Silicon Heterojunction Photodiodes
Authors:
Sarah Riazimehr,
Melkamu Belete,
Satender Kataria,
Olof Engström,
Max Christian Lemme
Abstract:
Heterostructures of two-dimensional (2D) and three-dimensional (3D) materials form efficient devices for utilizing the properties of both classes of materials. Graphene/silicon (G/Si) Schottky diodes have been studied extensively with respect to their optoelectronic properties. Here, we introduce a method to analyze measured capacitance-voltage data of G/Si Schottky diodes connected in parallel wi…
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Heterostructures of two-dimensional (2D) and three-dimensional (3D) materials form efficient devices for utilizing the properties of both classes of materials. Graphene/silicon (G/Si) Schottky diodes have been studied extensively with respect to their optoelectronic properties. Here, we introduce a method to analyze measured capacitance-voltage data of G/Si Schottky diodes connected in parallel with G/silicon dioxide/Si (GIS) capacitors. We also demonstrate the accurate extraction of the built-in potential ($Φ$$_{bi}$) and the Schottky barrier height from the measurement data independent of the Richardson constant.
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Submitted 25 February, 2020;
originally announced February 2020.
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Electron Transport across Vertical Silicon / MoS${_2}$ / Graphene Heterostructures: Towards Efficient Emitter Diodes for Graphene-Base Hot Electron Transistors
Authors:
Melkamu Belete,
Olof Engström,
Sam Vaziri,
Gunther Lippert,
Mindaugas Lukosius,
Satender Kataria,
Max C. Lemme
Abstract:
Heterostructures comprising of silicon (Si), molybdenum disulfide (MoS${_2}$) and graphene are investigated with respect to the vertical current conduction mechanism. The measured current-voltage (I-V) characteristics exhibit temperature dependent asymmetric current, indicating thermally activated charge carrier transport. The data is compared and fitted to a current transport model that confirms…
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Heterostructures comprising of silicon (Si), molybdenum disulfide (MoS${_2}$) and graphene are investigated with respect to the vertical current conduction mechanism. The measured current-voltage (I-V) characteristics exhibit temperature dependent asymmetric current, indicating thermally activated charge carrier transport. The data is compared and fitted to a current transport model that confirms thermionic emission as the responsible transport mechanism across the devices. Theoretical calculations in combination with the experimental data suggest that the heterojunction barrier from Si to MoS${_2}$ is linearly temperature dependent for T = 200 to 300 K with a positive temperature coefficient. The temperature dependence may be attributed to a change in band gap difference between Si and MoS${_2}$, strain at the Si/MoS${_2}$ interface or different electron effective masses in Si and MoS${_2}$, leading to a possible entropy change stemming from variation in density of states as electrons move from Si to MoS${_2}$. The low barrier formed between Si and MoS${_2}$ and the resultant thermionic emission demonstrated here makes the present devices potential candidates as the emitter diode of graphene-base hot electron transistors for future high-speed electronics.
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Submitted 23 December, 2019;
originally announced December 2019.
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Few-Layer MoS$_2$/a-Si:H Heterojunction pin-Photodiodes for extended Infrared Detection
Authors:
Andreas Bablich,
Daniel S. Schneider,
Paul Kienitz,
Satender Kataria,
Stefan Wagner,
Chanyoung Yim,
Niall McEvoy,
Olof Engstrom,
Julian Müller,
Yilmaz Sakalli,
Benjamin Butz,
Georg S. Duesberg,
Peter Haring Bolívar,
Max C. Lemme
Abstract:
Few-layer molybdenum disulfide (FL-MoS$_2$) films have been integrated into amorphous silicon (a-Si:H) pin photodetectors. To achieve this, vertical a-Si:H photodiodes were grown by plasma-enhanced chemical vapor deposition (PE-CVD) on top of large-scale synthesized and transferred homogeneous FL-MoS$_2$. This novel detector array exhibits long-term stability (more than six month) and outperforms…
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Few-layer molybdenum disulfide (FL-MoS$_2$) films have been integrated into amorphous silicon (a-Si:H) pin photodetectors. To achieve this, vertical a-Si:H photodiodes were grown by plasma-enhanced chemical vapor deposition (PE-CVD) on top of large-scale synthesized and transferred homogeneous FL-MoS$_2$. This novel detector array exhibits long-term stability (more than six month) and outperforms conventional silicon-based pin photodetectors in the infrared range (IR, $λ$ = 2120 nm) in terms of sensitivities by up to 50 mAW$^{-1}$. Photodetectivities of up to 2 x 10$^{10}$ Jones and external quantum efficiencies of 3 % are achieved. The detectors further feature the additional functionality of bias-dependent responsivity switching between the different spectral ranges. The realization of such scalable detector arrays is an essential step towards pixelated and wavelength-selective sensors operating in the IR spectral range.
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Submitted 22 July, 2019;
originally announced July 2019.
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Monolithically Integrated Perovskite Semiconductor Lasers on Silicon Photonic Chips by Scalable Top-Down Fabrication
Authors:
Piotr J Cegielski,
Anna Lena Giesecke,
Stefanie Neutzner,
Caroline Porschatis,
Marina Gandini,
Daniel Schall,
Carlo AR Perini,
Jens Bolten,
Stephan Suckow,
Satender Kataria,
Bartos Chmielak,
Thorsten Wahlbrink,
Annamaria Petrozza,
Max C Lemme
Abstract:
Metal-halide perovskites are promising lasing materials for realization of monolithically integrated laser sources, the key components of silicon photonic integrated circuits (PICs). Perovskites can be deposited from solution and require only low temperature processing leading to significant cost reduction and enabling new PIC architectures compared to state-of-the-art lasers realized through cost…
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Metal-halide perovskites are promising lasing materials for realization of monolithically integrated laser sources, the key components of silicon photonic integrated circuits (PICs). Perovskites can be deposited from solution and require only low temperature processing leading to significant cost reduction and enabling new PIC architectures compared to state-of-the-art lasers realized through costly and inefficient hybrid integration of III-V semiconductors. Until now however, due to the chemical sensitivity of perovskites, no microfabrication process based on optical lithography and therefore on existing semiconductor manufacturing infrastructure has been established. Here, the first methylammonium lead iodide perovskite micro-disc lasers monolithically integrated into silicon nitride PICs by such a top-down process is presented. The lasers show a record low lasing threshold of 4.7 $μ$Jcm$^{-2}$ at room temperature for monolithically integrated lasers, which are CMOS compatible and can be integrated in the back-end-of-line (BEOL) processes.
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Submitted 18 July, 2019;
originally announced July 2019.
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Dielectric Properties and Ion Transport in Layered MoS_{2} Grown by Vapor-Phase Sulfurization
Authors:
M. Belete,
S. Kataria,
U. Koch,
M. Kruth,
C. Engelhard,
J. Mayer,
O. Engström,
M. C. Lemme
Abstract:
Electronic and dielectric properties of vapor-phase grown MoS_{2} have been investigated in metal/MoS_{2}/silicon capacitor structures by capacitance-voltage and conductancevoltage techniques. Analytical methods confirm the MoS_{2} layered structure, the presence of interfacial silicon oxide (SiO_{x}) and the composition of the films. Electrical characteristics in combination with theoretical cons…
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Electronic and dielectric properties of vapor-phase grown MoS_{2} have been investigated in metal/MoS_{2}/silicon capacitor structures by capacitance-voltage and conductancevoltage techniques. Analytical methods confirm the MoS_{2} layered structure, the presence of interfacial silicon oxide (SiO_{x}) and the composition of the films. Electrical characteristics in combination with theoretical considerations quantify the concentration of electron states at the interface between Si and a 2.5 - 3 nm thick silicon oxide interlayer between Si and MoS_{2}. Measurements under electric field stress indicate the existence of mobile ions in MoS_{2} that interact with interface states. Based on time-offlight secondary ion mass spectrometry, we propose OH^{-} ions as probable candidates responsible for the observations. The dielectric constant of the vapor-phase grown MoS_{2} extracted from CV measurements at 100 KHz is in the range of 2.6 to 2.9. The present study advances the understanding of defects and interface states in MoS_{2}. It also indicates opportunities for ion-based plasticity in 2D material devices for neuromorphic computing applications.
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Submitted 19 July, 2018;
originally announced July 2018.
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Highly sensitive electromechanical piezoresistive pressure sensors based on large-area layered PtSe$_{2}$ films
Authors:
Stefan Wagner,
Chanyoung Yim,
Niall McEvoy,
Satender Kataria,
Volkan Yokaribas,
Agnieszka Kuc,
Stephan Pindl,
Claus-Peter Fritzen,
Thomas Heine,
Georg S. Duesberg,
Max C. Lemme
Abstract:
Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe$_{2}$), an exciting and unexplored 2D transition metal dichalcogenides (TMD) material, is particularly interesting because its scalable and low temperature growth process is compatible with silicon technology. Here, we explore the poten…
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Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe$_{2}$), an exciting and unexplored 2D transition metal dichalcogenides (TMD) material, is particularly interesting because its scalable and low temperature growth process is compatible with silicon technology. Here, we explore the potential of thin PtSe$_{2}$ films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe$_{2}$ films grown by thermally assisted conversion of Pt at a CMOS-compatible temperature of 400°C. We report high negative gauge factors of up to -84.8 obtained experimentally from PtSe$_{2}$ strain gauges in a bending cantilever beam setup. Integrated NEMS piezoresistive pressure sensors with freestanding PMMA/PtSe$_{2}$ membranes confirm the negative gauge factor and exhibit very high sensitivity, outperforming previously reported values by orders of magnitude. We employ density functional theory (DFT) calculations to understand the origin of the measured negative gauge factor. Our results suggest PtSe$_{2}$ as a very promising candidate for future NEMS applications, including integration into CMOS production lines.
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Submitted 19 March, 2018;
originally announced March 2018.
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Growth-Induced Strain in Chemical Vapor Deposited Monolayer MoS2: Experimental and Theoretical Investigation
Authors:
Satender Kataria,
Stefan Wagner,
Teresa Cusati,
Alessandro Fortunelli,
Giuseppe Iannaccone,
Himadri Pandey,
Gianluca Fiori,
Max C. Lemme
Abstract:
Monolayer molybdenum disulphide (MoS$_2$) is a promising two-dimensional (2D) material for nanoelectronic and optoelectronic applications. The large-area growth of MoS$_2$ has been demonstrated using chemical vapor deposition (CVD) in a wide range of deposition temperatures from 600 °C to 1000 °C. However, a direct comparison of growth parameters and resulting material properties has not been made…
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Monolayer molybdenum disulphide (MoS$_2$) is a promising two-dimensional (2D) material for nanoelectronic and optoelectronic applications. The large-area growth of MoS$_2$ has been demonstrated using chemical vapor deposition (CVD) in a wide range of deposition temperatures from 600 °C to 1000 °C. However, a direct comparison of growth parameters and resulting material properties has not been made so far. Here, we present a systematic experimental and theoretical investigation of optical properties of monolayer MoS$_2$ grown at different temperatures. Micro-Raman and photoluminescence (PL) studies reveal observable inhomogeneities in optical properties of the as-grown single crystalline grains of MoS$_2$. Close examination of the Raman and PL features clearly indicate that growth-induced strain is the main source of distinct optical properties. We carry out density functional theory calculations to describe the interaction of growing MoS$_2$ layers with the growth substrate as the origin of strain. Our work explains the variation of band gap energies of CVD-grown monolayer MoS$_2$, extracted using PL spectroscopy, as a function of deposition temperature. The methodology has general applicability to model and predict the influence of growth conditions on strain in 2D materials.
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Submitted 1 March, 2017;
originally announced March 2017.
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Non-invasive Scanning Raman Spectroscopy and Tomography for Graphene Membrane Characterization
Authors:
Stefan Wagner,
Thomas Dieing,
Alba Centeno,
Amaia Zurutuza,
Anderson D. Smith,
Mikael Östling,
Satender Kataria,
Max C. Lemme
Abstract:
Graphene has extraordinary mechanical and electronic properties, making it a promising material for membrane based nanoelectromechanical systems (NEMS). Here, chemical-vapor-deposited graphene is transferred onto target substrates to suspend it over cavities and trenches for pressure-sensor applications. The development of such devices requires suitable metrology methods, i.e., large-scale charact…
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Graphene has extraordinary mechanical and electronic properties, making it a promising material for membrane based nanoelectromechanical systems (NEMS). Here, chemical-vapor-deposited graphene is transferred onto target substrates to suspend it over cavities and trenches for pressure-sensor applications. The development of such devices requires suitable metrology methods, i.e., large-scale characterization techniques, to confirm and analyze successful graphene transfer with intact suspended graphene membranes. We propose fast and noninvasive Raman spectroscopy mapping to distinguish between freestanding and substrate-supported graphene, utilizing the different strain and doping levels. The technique is expanded to combine two-dimensional area scans with cross-sectional Raman spectroscopy, resulting in three-dimensional Raman tomography of membrane-based graphene NEMS. The potential of Raman tomography for in-line monitoring is further demonstrated with a methodology for automated data analysis to spatially resolve the material composition in micrometer-scale integrated devices, including free-standing and substrate-supported graphene. Raman tomography may be applied to devices composed of other two-dimensional materials as well as silicon micro- and nanoelectromechanical systems.
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Submitted 24 February, 2017;
originally announced February 2017.
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High Photocurrent in Gated Graphene-Silicon Hybrid Photodiodes
Authors:
Sarah Riazimehr,
Satender Kataria,
Rainer Bornemann,
Peter Haring Bolivar,
Francisco Javier Garcia Ruiz,
Olof Engström,
Andres Godoy,
Max Christian Lemme
Abstract:
Graphene/silicon (G/Si) heterojunction based devices have been demonstrated as high responsivity photodetectors that are potentially compatible with semiconductor technology. Such G/Si Schottky junction diodes are typically in parallel with gated G/silicon dioxide (SiO$_2$)/Si areas, where the graphene is contacted. Here, we utilize scanning photocurrent measurements to investigate the spatial dis…
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Graphene/silicon (G/Si) heterojunction based devices have been demonstrated as high responsivity photodetectors that are potentially compatible with semiconductor technology. Such G/Si Schottky junction diodes are typically in parallel with gated G/silicon dioxide (SiO$_2$)/Si areas, where the graphene is contacted. Here, we utilize scanning photocurrent measurements to investigate the spatial distribution and explain the physical origin of photocurrent generation in these devices. We observe distinctly higher photocurrents underneath the isolating region of graphene on SiO$_2$ adjacent to the Schottky junction of G/Si. A certain threshold voltage (V$_T$) is required before this can be observed, and its origins are similar to that of the threshold voltage in metal oxide semiconductor field effect transistors. A physical model serves to explain the large photocurrents underneath SiO$_2$ by the formation of an inversion layer in Si. Our findings contribute to a basic understanding of graphene / semiconductor hybrid devices which, in turn, can help in designing efficient optoelectronic devices and systems based on such 2D/3D heterojunctions.
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Submitted 30 May, 2017; v1 submitted 4 February, 2017;
originally announced February 2017.
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Carrier mediated reduction of stiffness in nanoindented crystalline Si(100)
Authors:
S. Kataria,
Sandip Dhara,
S. Dash,
A. K. Tyagi
Abstract:
We report the observation of carrier mediated decrease in the stiffness of crystalline (c)-Si(100) under nanoindentation. The apparent elastic modulii of heavily dopes (1E21 cm-3) p- and n-type c-Si are observed to be lower by 5.-7.5 percent that the estimated value for intrinsic (1E14 cm-3) c-Si. The deviation observed with respect to elastic modulus remarkably matches with the estimated value wh…
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We report the observation of carrier mediated decrease in the stiffness of crystalline (c)-Si(100) under nanoindentation. The apparent elastic modulii of heavily dopes (1E21 cm-3) p- and n-type c-Si are observed to be lower by 5.-7.5 percent that the estimated value for intrinsic (1E14 cm-3) c-Si. The deviation observed with respect to elastic modulus remarkably matches with the estimated value while considering the electronic elastic strain effect on carrier concentration as an influence of negative pressure coefficient of band gap for Si. The value is predominantly higher than the reported value of a decrease of 1-3 percent in stiffness as an effect of impurity in c-Si.
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Submitted 11 May, 2016;
originally announced May 2016.
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Resistive Graphene Humidity Sensors with Rapid and Direct Electrical Readout
Authors:
Anderson David Smith,
Karim Elgammal,
Frank Niklaus,
Anna Delin,
Andreas Fischer,
Sam Vaziri,
Fredrik Forsberg,
Mikael Råsander,
Håkan W. Hugosson,
Lars Bergqvist,
Stephan Schröder,
Satender Kataria,
Mikael Östling,
Max C. Lemme
Abstract:
We demonstrate humidity sensing using a change of electrical resistance of a single- layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N2), oxygen (O2), and argon (Ar). In order…
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We demonstrate humidity sensing using a change of electrical resistance of a single- layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N2), oxygen (O2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. Results from the interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO2 substrate, which in turn leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical read out and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.
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Submitted 25 October, 2015;
originally announced October 2015.
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Spectral Sensitivity of Graphene/Silicon Heterojunction Photodetectors
Authors:
Sarah Riazimehr,
Andreas Bablich,
Daniel Schneider,
Satender Kataria,
Vikram Passi,
Chanyoung Yim,
Georg S. Duesberg,
Max C. Lemme
Abstract:
We have studied the optical properties of two-dimensional (2D) Schottky photodiode heterojunctions made of chemical vapor deposited (CVD) graphene on n- and p-type Silicon (Si) substrates. Much better rectification behavior is observed from the diodes fabricated on n- Si substrates in comparison with the devices on p-Si substrates in dark condition. Also, graphene/n-Si photodiodes show a considera…
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We have studied the optical properties of two-dimensional (2D) Schottky photodiode heterojunctions made of chemical vapor deposited (CVD) graphene on n- and p-type Silicon (Si) substrates. Much better rectification behavior is observed from the diodes fabricated on n- Si substrates in comparison with the devices on p-Si substrates in dark condition. Also, graphene/n-Si photodiodes show a considerable responsivity of 270 mA/W within the silicon spectral range in DC reverse bias condition. The present results are furthermore compared with that of a molybdenum disulfide (MoS2)/p-type silicon photodiodes.
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Submitted 3 September, 2015;
originally announced September 2015.
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Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene
Authors:
Grzegorz Lupina,
Julia Kitzmann,
Ioan Costina,
Mindaugas Lukosius,
Christian Wenger,
Andre Wolff,
Sam Vaziri,
Mikael Ostling,
Iwona Pasternak,
Aleksandra Krajewska,
Wlodek Strupinski,
Satender Kataria,
Amit Gahoi,
Max C. Lemme,
Guenther Ruhl,
Guenther Zoth,
Oliver Luxenhofer,
Wolfgang Mehr
Abstract:
Integration of graphene with Si microelectronics is very appealing by offering potentially a broad range of new functionalities. New materials to be integrated with Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etch and electrochemical delamination methods with…
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Integration of graphene with Si microelectronics is very appealing by offering potentially a broad range of new functionalities. New materials to be integrated with Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etch and electrochemical delamination methods with respect to residual sub-monolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection x-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10$^{13}$ atoms/cm$^{2}$. These metal impurities appear to be partly mobile upon thermal treatment as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics these results reveal that further progress in synthesis, handling, and cleaning of graphene is required on the way to its advanced electronic and optoelectronic applications.
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Submitted 5 May, 2015;
originally announced May 2015.