Showing 1–17 of 17 results for author: Alberi, K

Toward Tunable Magnetic Dirac Semimetals: Mn Doping of Cd$_3$As$_2$

Authors: Anthony D. Rice, Ian Leahy, Herve Ness, Andrew G. Norman, Karen N. Heinselman, Chun-Sheng Jiang, David Graf, Alexey Suslov, Stephan Lany, Mark Van Schilfgaarde, Kirstin Alberi

Abstract: Magnetic impurities provide a route toward increasing functionality in electronic materials, often enabling new device concepts and architectures. In the case of topological semimetals, dilute magnetic doping presents a particularly attractive approach for inducing a Dirac to Weyl phase change via time reversal symmetry breaking. However, efforts to realize changes in the electronic structure have… ▽ More Magnetic impurities provide a route toward increasing functionality in electronic materials, often enabling new device concepts and architectures. In the case of topological semimetals, dilute magnetic doping presents a particularly attractive approach for inducing a Dirac to Weyl phase change via time reversal symmetry breaking. However, efforts to realize changes in the electronic structure have been limited by challenges in incorporating magnetic impurities into crystals with sufficiently high electron mobilities to detect them via transport or spectroscopic techniques. Here, we demonstrate incorporation of Mn into Cd$_3$As$_2$ Dirac semimetal thin films grown by molecular beam epitaxy (MBE). Using As-rich growth conditions and [001] oriented thin films, Mn compositions of >10% are achieved. Films contain uniform distributions of Mn with no evidence of secondary phases and exhibit electron mobilities greater than 10,000-30,000 cm$^2$/Vs up to 5% Mn. An evolution in the magnetization behavior along with the emergence of a second quantum oscillation frequency at low Mn concentrations provide preliminary evidence of Mn-induced changes in the electronic structure that are consistent with a Weyl phase. This work demonstrates the potential of magnetically doping topological semimetal thin films and a pathway for synthesizing them. △ Less

Submitted 26 January, 2026; originally announced January 2026.

Chirality-induced magnetoresistance in hybrid organic-inorganic perovskite semiconductors

Authors: Md Azimul Haque, Pius Markus Theiler, Ian A. Leahy, Steven P. Harvey, Jeiwan Tan, Matthew P Hautzinger, Margherita Taddei, Aeron McConnell, Andrew Greider, Andrew H. Comstock, Yifan Dong, Kirstin Alberi, Yuan Ping, Peter C. Sercel, Joseph M. Luther, Dali Sun, Matthew C. Beard

Abstract: The combination of semiconducting properties and synthetically tunable chirality in chiral metal halide semiconductors (CMHS) offer a compelling platform for room temperature control over electronic spin properties, leveraging effects such as chirality-induced spin selectivity (CISS) for the development of new opto-spintronic functionalities. We report room-temperature CISS-induced magnetoresistan… ▽ More The combination of semiconducting properties and synthetically tunable chirality in chiral metal halide semiconductors (CMHS) offer a compelling platform for room temperature control over electronic spin properties, leveraging effects such as chirality-induced spin selectivity (CISS) for the development of new opto-spintronic functionalities. We report room-temperature CISS-induced magnetoresistance (CISS-MR) exceeding 100% for spin valves in a configuration consisting of a ferromagnet (FM), tunneling barrier, and CMHS. The high CISS-MR is attributed to interfacial spin-selective tunneling barrier induced by the chirality, which can produce current dissymmetry factors that surpass the limit imposed by the Jullière model governed by the intrinsic spin polarization of the adjacent FM contact. The CISS-MR exhibits a strong dependence on the CMHS composition, revealing a structure-property relationship between CISS and structural chirality. The observed exceptionally large tunneling MR response differentiates from a subtle anisotropic MR arising from the proximity effect at the FM/CMHS interface in the absence of a tunneling barrier. Our study provides insights into charge-to-spin interconversion in chiral semiconductors, offering materials design principles to control and enhance CISS response and utilize it in functional platforms. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Report number: MR-01

Origin of metal-insulator transition in rare-earth Nickelates

Authors: Swagata Acharya, Brooks Tellekamp, Jerome Jackson, Dimitar Pashov, Jeffrey L. Blackburn, Kirstin Alberi, Mark van Schilfgaarde

Abstract: Rare-earth nickelates RNiO3 (R=rare-earth element) exhibit three kinds of phase transitions with decreasing temperature: a structural transition from a pseudo-cubic to a monoclinic phase, a metal- insulator transition (MIT), and a magnetic transition from a paramagnetic state to an ordered one. The first two occur at the same temperature, which has led to a consensus that the MIT is driven by latt… ▽ More Rare-earth nickelates RNiO3 (R=rare-earth element) exhibit three kinds of phase transitions with decreasing temperature: a structural transition from a pseudo-cubic to a monoclinic phase, a metal- insulator transition (MIT), and a magnetic transition from a paramagnetic state to an ordered one. The first two occur at the same temperature, which has led to a consensus that the MIT is driven by lattice distortions. We show here that the primary driving force for the MIT is magnetic; however because of the unusual d7 configuration of Ni, additional flexibility in spin configurations are also needed which symmetry-lowing structural deformations make possible. The latter enable Ni to disproportionate into two kinds: a high-spin and a low-spin configuration, which allow the system to reduce its unfavorable orbital moment and also open a gap. △ Less

Submitted 18 November, 2025; originally announced November 2025.

Robust and Symmetric Magnetic Field Dependency of Superconducting Diode Effect in Asymmetric Dirac Semimetal SQUIDs

Authors: H. C. Travaglini, J. J. Cuozzo, K. R. Sapkota, I. A. Leahy, A. D. Rice, K. Alberi, W. Pan

Abstract: The recent demonstration of the superconducting diode effect (SDE) has generated renewed interests in superconducting electronics in which devices such as compact superconducting diodes that can perform signal rectification where low-energy operations are needed. In this article, we present our results of robust and symmetric-in-magnetic-field SDE in asymmetric superconducting quantum interference… ▽ More The recent demonstration of the superconducting diode effect (SDE) has generated renewed interests in superconducting electronics in which devices such as compact superconducting diodes that can perform signal rectification where low-energy operations are needed. In this article, we present our results of robust and symmetric-in-magnetic-field SDE in asymmetric superconducting quantum interference devices (SQUIDs) realized in high-quality Dirac semimetal Cd3As2 thin film grown by the molecular beam epitaxy (MBE) technique. Consistent with previous work, a zero magnetic field SDE is observed. Furthermore, the difference in switching current is independent of the strength and polarity of an out-plane magnetic field in the range of -10 mT and 10 mT. We speculate that this robust symmetric-in-field SDE in our Dirac semimetal SQUIDs is due to the formation of helical spin texture, theoretically predicted in Dirac semimetals. △ Less

Submitted 27 May, 2025; originally announced May 2025.

Comments: accepted to APL Quantum

Doping Topological Dirac Semimetal with magnetic impurities: electronic structure of Mn-doped Cd$_3$As$_2$

Authors: H. Ness, I. Leahy, A. Rice, D. Pashov, K. Alberi, M. van Schilfgaarde

Abstract: The prospect of transforming a Dirac topological semimetal (TSM) into a Weyl TSM phase, following doping by magnetic impurities, is central to TSM applications. The magnetic field from polarized $d$ levels of magnetic impurities produces a field with a sharp local structure. To what extent magnetic impurities act in the same manner as an applied field and what are the effects of such a field on th… ▽ More The prospect of transforming a Dirac topological semimetal (TSM) into a Weyl TSM phase, following doping by magnetic impurities, is central to TSM applications. The magnetic field from polarized $d$ levels of magnetic impurities produces a field with a sharp local structure. To what extent magnetic impurities act in the same manner as an applied field and what are the effects of such a field on the electronic structure of a Dirac TSM is the subject of this paper. We present electronic structure calculations of bulk Cd$_3$As$_2$ with substitutional doping of Mn impurities in the dilute alloy range. Quasi-particle $GW$ (QS$GW$) ab-initio electronic structure calculations are used in conjunction with $k \cdot p$ model Hamiltonian calculations. As expected, we observe the splitting of the Dirac points into pairs of Weyl points following the doping with Mn. We also show that the electronic structure of Mn-doped Cd$_3$As$_2$ can be emulated by the electronic structure of pristine Cd$_3$As$_2$ with an appropriate external magnetic field. Some properties of the conductivity of bulk Cd$_3$As$_2$ for different magnetic field orientations are also investigated. Our results inform future opportunities for unique device functionality based on band structure tuning not found in conventional magnetic Weyl TSM. △ Less

Submitted 10 May, 2025; originally announced May 2025.

Report number: revised version accepted for publication (open access) in Phys. Rev. Research 7, 033261 (2025)

Interplay of Quasi-Quantum Hall Effect and Coulomb Disorder in Semimetals

Authors: Ian A. Leahy, Anthony D. Rice, Jocienne N. Nelson, Herve Ness, Mark van Schilfgaarde, David Graf, Alexey Suslov, Wei Pan, Kirstin Alberi

Abstract: Low carrier densities in topological semimetals (TSMs) enable the exploration of novel magnetotransport in the quantum limit (QL). Recent findings consistent with 3D quasi-quantum Hall effect (QQHE) have positioned TSMs as promising platforms for exploring 3D quantum Hall transport, but the lack of tunability in the Fermi level has thus far limited the ability to observe a QQHE signal. Here, we tu… ▽ More Low carrier densities in topological semimetals (TSMs) enable the exploration of novel magnetotransport in the quantum limit (QL). Recent findings consistent with 3D quasi-quantum Hall effect (QQHE) have positioned TSMs as promising platforms for exploring 3D quantum Hall transport, but the lack of tunability in the Fermi level has thus far limited the ability to observe a QQHE signal. Here, we tune the defect concentrations in the Dirac semimetal Cd${}_3$As${}_2$ to achieve ultra-low carrier concentrations at 2 K around $2.9\times10^{16}$cm${}^{-3}$, giving way to QQHE signal at modest fields near 10 T. At low carrier densities, where QQHE is most accessible, we find that clear QQHE is obscured by a carrier density dependent background originating from Coulomb disorder from charged point defects and Landau level broadening. Our results highlight the interplay between QQHE and Coulomb disorder, demonstrating that clear observation of QQHE in TSMs intricately depends on Fermi level and disorder magnitudes. We find that Coulomb disorder, as theoretically predicted, is an essential ingredient for understanding the magnetoresistivity for a spectrum of Fermi levels in Cd${}_3$As${}_2$, anchoring the role of defects and charged disorder in TSM applications. We discuss future constraints and opportunities in exploring 3D QQHE and quantum Hall effects in TSMs. △ Less

Submitted 29 December, 2025; v1 submitted 6 December, 2024; originally announced December 2024.

Spin injection across a III-V/chiral perovskite interface enabling spin accumulation at room temperature

Authors: Matthew P. Hautzinger, Xin Pan, Steven C. Hayden, Jiselle Y. Ye, Qi Jiang, Mickey J. Wilson, Yifan Dong, Emily K. Raulerson, Ian A. Leahy, Chun-Sheng Jiang, Joseph M. Luther, Yuan Lu, Katherine Jungjohann, Z. Valy Vardeny, Joseph J. Berry, Kirstin Alberi, Matthew C. Beard

Abstract: Spin accumulation in semiconductor structures at room temperature and without magnetic fields is key to enable a broader range of opto-electronic functionality. Current efforts are limited due to inherent inefficiencies associated with spin injection into semiconductor structures. Here, we demonstrate spin injection across chiral halide perovskite/III-V interfaces achieving spin accumulation in a… ▽ More Spin accumulation in semiconductor structures at room temperature and without magnetic fields is key to enable a broader range of opto-electronic functionality. Current efforts are limited due to inherent inefficiencies associated with spin injection into semiconductor structures. Here, we demonstrate spin injection across chiral halide perovskite/III-V interfaces achieving spin accumulation in a standard semiconductor III-V (AlxGa1-x)0.5In0.5P multiple quantum well (MQW) light emitting diode (LED). The spin accumulation in the MQW is detected via emission of circularly polarized light with a degree of polarization of up to ~15%. The chiral perovskite/III-V interface was characterized with X-ray photoemission spectroscopy (XPS), cross sectional scanning Kelvin probe force microscopy, and cross section transmission electron microscopy (TEM) imaging, showing a clean semiconductor/semiconductor interface where the fermi-level can equilibrate. These findings demonstrate chiral perovskite semiconductors can transform well-developed semiconductor platforms to ones that can also control spin. △ Less

Submitted 14 November, 2023; v1 submitted 8 September, 2023; originally announced September 2023.

Thin film TaAs: developing a platform for Weyl semimetal devices

Authors: Jocienne N. Nelson, Anthony D. Rice, Rafal Kurleto, Amanda Shackelford, Zachary Sierzega, Chun-Sheng Jiang, Andrew G. Norman, Megan E. Holtz, John S. Mangum, Ian A. Leahy, Karen N. Heinselman, Herve Ness, Mark Van Schilfgaarde, Daniel S. Dessau, Kirstin Alberi

Abstract: MX monopnictide compounds (M=Nb,Ta, X = As,P) are prototypical three-dimensional Weyl semimetals (WSMs) that have been shown in bulk single crystal form to have potential for a wide variety of novel devices due to topologically protected band structures and high mobilities. However, very little is known about thin film synthesis, which is essential to enable device applications. We synthesize TaAs… ▽ More MX monopnictide compounds (M=Nb,Ta, X = As,P) are prototypical three-dimensional Weyl semimetals (WSMs) that have been shown in bulk single crystal form to have potential for a wide variety of novel devices due to topologically protected band structures and high mobilities. However, very little is known about thin film synthesis, which is essential to enable device applications. We synthesize TaAs(001) epilayers by molecular beam epitaxy on GaAs(001) and provide an experimental phase diagram illustrating conditions for single phase, single-crystal-like growth. We investigate the relationship between nanoscale defects and electronic structure, using angle-resolved photoemission spectroscopy, Kelvin probe microscopy and transmission electron microscopy. Our results provide a roadmap and platform for developing 3D WSMs for device applications. △ Less

Submitted 9 March, 2023; originally announced March 2023.

Comments: 12 pages, 5 figures

Direct link between disorder, mobility and magnetoresistance in topological semimetals

Authors: Jocienne N. Nelson, Anthony D. Rice, Chase Brooks, Ian A. Leahy, Glenn Teeter, Mark Van Schilfgaarde, Stephan Lany, Brian Fluegel, Minhyea Lee, Kirstin Alberi

Abstract: The extent to which disorder influences the properties of topological semimetals remains an open question and is relevant to both the understanding of topological states and the use of topological materials in practical applications. Here, we achieve unmatched and systematic control of point defect concentrations in the prototypical Dirac semimetal Cd$_3$As$_2$ to gain important insight into the r… ▽ More The extent to which disorder influences the properties of topological semimetals remains an open question and is relevant to both the understanding of topological states and the use of topological materials in practical applications. Here, we achieve unmatched and systematic control of point defect concentrations in the prototypical Dirac semimetal Cd$_3$As$_2$ to gain important insight into the role of disorder on electron transport behavior. We find that arsenic vacancies introduce localized states near the Fermi level and strongly influence the electron mobility. Reducing arsenic vacancies by changing the As/Cd flux ratio used during deposition results in an increase in the magnetoresistance from 200%-1000% and an increase in mobility from 5000-18,000 cm$^2$/Vs. However, the degree of linear magnetoresistance, which has previously been linked to disorder, is found here to correlate inversely with measures of disorder, including disorder potential and disorder correlation lengths. This finding yields important new information in the quest to identify the origin of linear magnetoresistance in a wider range of materials. △ Less

Submitted 20 June, 2022; originally announced June 2022.

Comments: 19 pages, 3 main figures, 4 supplemental figures

Journal ref: Phys. Rev. B 107, L220206 2023

Defects in Cd3As2 Epilayers Via Molecular Beam Epitaxy and Strategies for Reducing Them

Authors: Anthony Rice, Kwangwook Park, Eamonn Hughes, Kunal Mukherjee, Kirstin Alberi

Abstract: Molecular beam epitaxy offers an exciting avenue for investigating the behavior of topological semimetal Cd3As2, by providing routes for doping, alloying, strain engineering, and heterostructure formation. To date, however, minimal exploration has been devoted to the impact of defects that are incorporated into epilayers due to contraints imposed by the substrate and narrow growth window. Here, we… ▽ More Molecular beam epitaxy offers an exciting avenue for investigating the behavior of topological semimetal Cd3As2, by providing routes for doping, alloying, strain engineering, and heterostructure formation. To date, however, minimal exploration has been devoted to the impact of defects that are incorporated into epilayers due to contraints imposed by the substrate and narrow growth window. Here, we use a combination of lattice-matched ZnxCd1-xTe buffer layers, miscut substrates and broadband illumination to study how dislocations, twins and point defects influence the electron mobility of Cd3As2. A combination of defect suppression approaches produces Cd3As2 epilayers with electron mobilities upwards of 15,000 cm2/V-s at room temperature. △ Less

Submitted 3 September, 2019; originally announced September 2019.

Journal ref: Phys. Rev. Materials 3, 121201 (2019)

Photoassisted physical vapor epitaxial growth of semiconductors: a review of light-induced modifications to growth processes

Authors: Kirstin Alberi, Michael A. Scarpulla

Abstract: Herein we review the remarkable range of modifications to materials properties associated with photoexcitation of the growth surface during physical vapor epitaxy of semiconductors. We concentrate on mechanisms producing measureable, utilizable changes in crystalline perfection, phase, composition, doping, and defect distribution. We outline the relevant physics of different mechanisms, concentrat… ▽ More Herein we review the remarkable range of modifications to materials properties associated with photoexcitation of the growth surface during physical vapor epitaxy of semiconductors. We concentrate on mechanisms producing measureable, utilizable changes in crystalline perfection, phase, composition, doping, and defect distribution. We outline the relevant physics of different mechanisms, concentrating on those yielding effects orthogonal to the primary growth variables of temperature and atomic or molecular fluxes and document the phenomenological effects reported. Based on experimental observations from a range of semiconductor systems and growth conditions, the primary effects include enhanced anion desorption, molecular dissociation, increased doping efficiency, modification to defect populations and improvements to the crystalline quality of epilayers grown at low temperatures. Future research directions and technological applications are also discussed. △ Less

Submitted 20 September, 2017; originally announced September 2017.

Tailoring Heterovalent Interface Formation with Light

Authors: Kwangwook Park, Kirstin Alberi

Abstract: Integrating different semiconductor materials into an epitaxial device structure offers additional degrees of freedom to select for optimal material properties in each layer. However, interface between materials with different valences (i.e. III-V, II-VI and IV semiconductors) can be difficult to form with high quality. Using ZnSe/GaAs as a model system, we explore the use of UV illumination durin… ▽ More Integrating different semiconductor materials into an epitaxial device structure offers additional degrees of freedom to select for optimal material properties in each layer. However, interface between materials with different valences (i.e. III-V, II-VI and IV semiconductors) can be difficult to form with high quality. Using ZnSe/GaAs as a model system, we explore the use of UV illumination during heterovalent interface growth by molecular beam epitaxy as a way to modify the interface properties. We find that UV illumination alters the mixture of chemical bonds at the interface, permitting the formation of Ga-Se bonds that help to passivate the underlying GaAs layer. Illumination also helps to reduce defects in the ZnSe epilayer. These results suggest that moderate UV illumination during growth may be used as a way to improve the optical properties of both the GaAs and ZnSe layers on either side of the interface. △ Less

Submitted 9 May, 2017; originally announced May 2017.

Comments: 23 pages, 7 figures

Effects of excess carriers on native defects in wide bandgap semiconductors: illumination as a method to enhance p-type doping

Authors: Kirstin Alberi, Michael A. Scarpulla

Abstract: Undesired unintentional doping and doping limits in semiconductors are typically caused by compensating defects with low formation energies. Since the formation energy of a charged defect depends linearly on the Fermi level, doping limits can be especially pronounced in wide bandgap semiconductors where the Fermi level can vary substantially. Introduction of non-equilibrium carrier concentrations… ▽ More Undesired unintentional doping and doping limits in semiconductors are typically caused by compensating defects with low formation energies. Since the formation energy of a charged defect depends linearly on the Fermi level, doping limits can be especially pronounced in wide bandgap semiconductors where the Fermi level can vary substantially. Introduction of non-equilibrium carrier concentrations during growth or processing alters the chemical potentials of band carriers and thus provides the possibility of modifying populations of charged defects in ways impossible at thermal equilibrium. Herein we demonstrate that, for an ergodic system with excess carriers, the rates of carrier capture and emission involving a defect charge transition level rigorously determine the admixture of electron and hole quasi-Fermi levels determining the formation energy of non-zero charge states of that defect type. To catalog the range of possible responses to excess carriers, we investigate the behavior of a single donor-like defect as functions of extrinsic doping and energy of the charge transition level. The technologically most important finding is that excess carriers will increase the formation energy of compensating defects for most values of the charge transition level in the bandgap. Thus, it may be possible to overcome limitations on doping imposed by native defects. Cases also exist in wide bandgap semiconductors in which the concentration of defects with the same charge polarity as the majority dopant is either left unchanged or actually increases. The causes of these various behaviors are rationalized in terms of the capture and emission rates and guidelines for carrying out experimental tests of this model are given. △ Less

Submitted 10 March, 2017; originally announced March 2017.

Ultra-low threshold polariton condensation

Authors: Mark Steger, Brian Fluegel, Kirstin Alberi, Angelo Mascarenhas, David W. Snoke, Loren N. Pfeiffer, Ken West

Abstract: We demonstrate condensation of microcavity polaritons with a very sharp threshold occuring at two orders of magnitude lower pump intensity than previous demonstrations of condensation. The long cavity-lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or "polariton lasing" has long been proposed as a promising source of cohere… ▽ More We demonstrate condensation of microcavity polaritons with a very sharp threshold occuring at two orders of magnitude lower pump intensity than previous demonstrations of condensation. The long cavity-lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or "polariton lasing" has long been proposed as a promising source of coherent light at lower threshold than traditional lasing, and these results suggest methods to bring this threshold even lower. △ Less

Submitted 26 September, 2016; originally announced September 2016.

Comments: 4 pages, one figure, one table

Suppression of compensating native defect formation during semiconductor processing via excess carriers

Authors: Kirstin Alberi, Michael A. Scarpulla

Abstract: In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are responsible in many cases, but extrinsic dopants may also act as their own compensation when occupying an alternate lattice site. Suppressing the concentrations of compensating defects during processing close to t… ▽ More In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are responsible in many cases, but extrinsic dopants may also act as their own compensation when occupying an alternate lattice site. Suppressing the concentrations of compensating defects during processing close to thermal equilibrium is difficult because formation enthalpies are lowered as the Fermi level moves towards the majority band edge. Excess carriers, introduced for example by photogeneration, modify the formation enthalpy of semiconductor defects and thus can be harnessed during crystal growth or annealing to suppress such defect populations. Herein we develop a rigorous and general model for defect formation in the presence of steady-state excess carrier concentrations by combining the standard quasi-chemical formalism with a detailed-balance description that is applicable for any defect state in the bandgap. Considering the quasi-Fermi levels as chemical potentials, we demonstrate that increasing the minority carrier concentration increases the formation enthalpy for typical compensating centers, thus suppressing their formation. This effect is illustrated for the specific example of native GaSb antisite acceptors in nominally un-doped and extrinsically n-type doped GaSb. The model also predicts reductions in the concentration of ionized scattering centers as well as increased mobility. While our treatment is generalized for excess carrier injection or generation in semiconductors by any means, we provide a set of guidelines for applying the concept in photoassisted physical vapor deposition. △ Less

Submitted 22 June, 2016; originally announced June 2016.

Journal ref: Scientific Reports 6, 27954 (2016)

Metal-insulator transition by isovalent anion substitution in Ga1-xMnxAs: Implications to ferromagnetism

Authors: P. R. Stone, K. Alberi, S. K. Z. Tardif, J. W. Beeman, K. M. Yu, W. Walukiewicz, O. D. Dubon

Abstract: We have investigated the effect of partial isovalent anion substitution in Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only 2.4% of As by P induces a metal-insulator transition at a constant Mn doping of x=0.046 while the replacement of 0.4 % As with N results in the crossover from metal to insulator for x=0.037. This remarkable behavior is consistent with a scenario i… ▽ More We have investigated the effect of partial isovalent anion substitution in Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only 2.4% of As by P induces a metal-insulator transition at a constant Mn doping of x=0.046 while the replacement of 0.4 % As with N results in the crossover from metal to insulator for x=0.037. This remarkable behavior is consistent with a scenario in which holes located within an impurity band are scattered by alloy disorder in the anion sublattice. The shorter mean free path of holes, which mediate ferromagnetism, reduces the Curie temperature TC from 113 K to 60 K (100 K to 65 K) upon the introduction of 3.1 % P (1% N) into the As sublattice. △ Less

Submitted 23 July, 2008; originally announced July 2008.

Comments: 16 pages, 4 figures

Journal ref: Phys. Rev. Lett. 101, 087203 (2008)

Fabrication of GaNxAs1-x Quantum Structures by Focused Ion Beam Patterning

Authors: K. Alberi, A. Minor, M. A. Scarpulla, S. J. Chung, D. E. Mars, K. M. Yu, W. Walukiewicz, O. D. Dubon

Abstract: A novel approach to the fabrication of GaNxAs1-x quantum dots and wires via ion beam patterning is presented. Photomodulated reflectance spectra confirm that N can be released from the As sublattice of an MBE-grown GaNxAs1-x film by amorphization through ion implantation followed by regrowth upon rapid thermal annealing (RTA). Amorphization may be achieved with a focused ion beam (FIB), which is… ▽ More A novel approach to the fabrication of GaNxAs1-x quantum dots and wires via ion beam patterning is presented. Photomodulated reflectance spectra confirm that N can be released from the As sublattice of an MBE-grown GaNxAs1-x film by amorphization through ion implantation followed by regrowth upon rapid thermal annealing (RTA). Amorphization may be achieved with a focused ion beam (FIB), which is used to implant Ga ions in patterned lines such that annealing produces GaAs regions within a GaNxAs1-x film. The profiles of these amorphized lines are dependent upon the dose implanted, and the film reaches a damage threshold during RTA due to excess Ga. By altering the FIB implantation pattern, quantum dots or wires may be fabricated. △ Less

Submitted 2 August, 2004; originally announced August 2004.

Comments: To appear in the proceedings of the 27th International Conference on the Physics of Semiconductors (ICPS-27, Flagstaff, AZ, July 26-30, 2004)