Center for Quantum Devices - Most Downloaded Journal Articles

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7.	III-Nitride/Ga2O3 heterostructure for future power electronics: opportunity and challenges Nirajman Shrestha, Jun Hee Lee, F. H. Teherani, Manijeh Razeghi Proc. of SPIE Vol. 12895, Quantum Sensing and Nano Electronics and Photonics XX, 128950B (28 January - 1 February 2024, San Francisco)http://dx.doi.org/10.1117/12.3011688 ...[Visit Journal] Ga2O3 has become the new focal point of high-power semiconductor device research due to its superior capability to handle high voltages in smaller dimensions and with higher efficiencies compared to other commercialized semiconductors. However, the low thermal conductivity of the material is expected to limit device performance. To compensate for the low thermal conductivity of Ga2O3 and to achieve a very high density 2-dimensional electron gas (2DEG), an innovative idea is to combine Ga2O3 with III-Nitrides (which have higher thermal conductivity), such as AlN. However, metal-polar AlN/β-Ga2O3 heterojunction provides type-II heterojunction which are beneficial for optoelectronic application, because of the negative value of specific charge density. On the other hand, N-polar AlN/β- Ga2O3 heterostructures provide higher 2DEG concentration and larger breakdown voltage compared to conventional AlGaN/GaN devices. This advancement would allow the demonstration of RF power transistors with a 10x increase in power density compared to today’s State of the Art (SoA) and provide a solution to size, weight, and power-constrained applications [reprint (PDF)]
7.	High Detectivity InGaAs/InGaP Quantum-Dot Infrared Photodetectors Grown by Low Pressure Metalorganic Chemical Vapor Deposition J. Jiang, S. Tsao, T. O'Sullivan, W. Zhang, H. Lim, T. Sills, K. Mi, M. Razeghi, G.J. Brown, and M.Z. Tidrow Applied Physics Letters, 84 (12)-- April 22, 2004 ...[Visit Journal] We report a high detectivity middle-wavelength infrared quantum dot infrared photodetector (QDIP). The InGaAs quantum dots were grown by self-assembly on an InGaP matrix via low pressure metalorganic chemical vapor deposition. Photoresponse was observed at temperatures above 200 K with a peak wavelength of 4.7 µm and cutoff wavelength of 5.2 µm. The background limited performance temperature was 140 K, and this was attributed to the super low dark current observed in this QDIP. A detectivity of 3.6×10¹⁰ cm·Hz^½/W, which is comparable to the state-of-the-art quantum well infrared photodetectors in a similar wavelength range, was obtained for this InGaAs/InGaP QDIP at both T = 77 K and T = 95 K at biases of –1.6 and –1.4 V, [reprint (PDF)]
7.	Surface leakage investigation via gated type-II InAs/GaSb long-wavelength infrared photodetectors G. Chen, E.K. Huang, A.M. Hoang, S. Bogdanov, S.R. Darvish, and M. Razeghi Applied Physics Letters, Vol. 101, No. 21, p. 213501-1-- November 19, 2012 ...[Visit Journal] By using gating technique, surface leakage generated by SiO₂ passivation in long-wavelength infrared type-II superlattice photodetector is suppressed, and different surface leakage mechanisms are disclosed. By reducing the SiO₂ passivation layer thickness, the saturated gated bias is reduced to −4.5 V. At 77 K, dark current densities of gated devices are reduced by more than 2 orders of magnitude, with 3071 Ω·cm² differential-resistance-area product at −100 mV. With quantum efficiency of 50%, the 11 μm 50% cut-off gated photodiode has a specific detectivity of 7 × 10¹¹ Jones, and the detectivity stays above 2 × 10¹¹ Jones from 0 to −500 mV operation bias. [reprint (PDF)]
7.	Thermal Conductivity of InAs/GaSb Type II Superlattice C. Zhou, B.M. Nguyen, M. Razeghi and M. Grayson Journal of Electronic Materials, Vol. 41, No. 9, p. 2322-2325-- August 1, 2012 ...[Visit Journal] The cross-plane thermal conductivity of a type II InAs/GaSb superlattice(T2SL) is measured from 13 K to 300 K using the 3x method. Thermal conductivity is reduced by up to two orders of magnitude relative to the GaSb bulk substrate. The low thermal conductivity of around 1 W/m K to 8 W/m K may serve as an advantage for thermoelectric applications at low temperatures, while presenting a challenge for T2SL interband cascade lasers and highpower photodiodes. We describe a power-law approximation to model nonlinearities in the thermal conductivity, resulting in increased or decreased peak temperature for negative or positive exponents, respectively. [reprint (PDF)]
6.	High-performance InP-based midinfrared quantum cascade lasers at Northwestern University M. Razeghi, Y. Bai, S. Slivken, and S.R. Darvish SPIE Optical Engineering, Vol. 49, No. 11, November 2010, p. 111103-1-- November 15, 2010 ...[Visit Journal] We present recent performance highlights of midinfrared quantum cascade lasers (QCLs) based on an InP material system. At a representative wavelength around 4.7 µm, a number of breakthroughs have been achieved with concentrated effort. These breakthroughs include watt-level continuous wave operation at room temperature, greater than 50% peak wall plug efficiency at low temperatures, 100-W-level pulsed mode operation at room temperature, and 10-W-level pulsed mode operation of photonic crystal distributed feedback quantum cascade lasers at room temperature. Since the QCL technology is wavelength adaptive in nature, these demonstrations promise significant room for improvement across a wide range of mid-IR wavelengths. [reprint (PDF)]
6.	Strain-Induced Metastable Phase Stabilization in Ga₂O₃ Thin Films Yaobin Xu, Ji-hyeon Park, Zhenpeng Yao, Christopher Wolverton, Manijeh Razeghi, Jinsong Wu, and Vinayak P. Dravid ACS Appl. Mater. Interfaces-- January 10, 2019 ...[Visit Journal] It is well known that metastable and transient structures in bulk can be stabilized in thin films via epitaxial strain (heteroepitaxy) and appropriate growth conditions that are often far from equilibrium. However, the mechanism of heteroepitaxy, particularly how the nominally unstable or metastable phase gets stabilized, remains largely unclear. This is especially intriguing for thin film Ga₂O₃, where multiple crystal phases may exist under varied growth conditions with spatial and dimensional constraints. Herein, the development and distribution of epitaxial strain at the Ga₂O₃/Al₂O₃ film-substrate interfaces is revealed down to the atomic resolution along different orientations, with an aberration-corrected scanning transmission electron microscope (STEM). Just a few layers of metastable α-Ga₂O₃ structure were found to accommodate the misfit strain in direct contact with the substrate. Following an epitaxial α-Ga₂O₃ structure of about couple unit cells, several layers (4~5) of transient phase appear as the intermediate structure to release the misfit strain. Subsequent to this transient crystal phase, the nominally unstable κ-Ga₂O₃ phase is stabilized as the major thin film phase form. We show that the epitaxial strain is gracefully accommodated by rearrangement of the oxygen polyhedra. When the structure is under large compressive strain, Ga3+ ions occupy only the oxygen octahedral sites to form a dense structure. With gradual release of the compressive strain, more and more Ga3+ ions occupy the oxygen tetrahedral sites, leading to volumetric expansion and the phase transformation. The structure of the transition phase is identified by high resolution electron microscopy (HREM) observation, complemented by the density functional theory (DFT) calculations. This study provides insights from the atomic scale and their implications for the design of functional thin film materials using epitaxial engineering.
6.	Near milliwatt power AlGaN-based ultraviolet light emitting diodes based on lateral epitaxial overgrowth of AlN on Si(111) Y. Zhang, S. Gautier, C. Cho, E. Cicek, Z, Vashaei, R. McClintock, C. Bayram, Y. Bai and M. Razeghi Applied Physics Letters, Vol. 102, No. 1, p. 011106-1-- January 7, 2013 ...[Visit Journal] We report on the growth, fabrication, and device characterization of AlGaN-based thin-film ultraviolet (UV) (λ ∼ 359 nm) light emitting diodes (LEDs). First, AlN/Si(111) template is patterned. Then, a fully coalesced 7-μm-thick lateral epitaxial overgrowth (LEO) of AlN layer is realized on patterned AlN/Si(111) template followed by UV LED epi-regrowth. Metalorganic chemical vapor deposition is employed to optimize LEO AlN and UV LED epitaxy. Back-emission UV LEDs are fabricated and flip-chip bonded to AlN heat sinks followed by Si(111) substrate removal. A peak pulsed power and slope efficiency of ∼0.6 mW and ∼1.3 μW/mA are demonstrated from these thin-film UV LEDs, respectively. For comparison, top-emission UV LEDs are fabricated and back-emission LEDs are shown to extract 50% more light than top-emission ones. [reprint (PDF)]
6.	Low pressure metalorganic chemical vapor deposition of InP and related compounds M. Razeghi, M. A. Poisson, J. P. Larivain & J. P. Duchemin Razeghi, M., Poisson, M.A., Larivain, J.P. et al. Low pressure metalorganic chemical vapor deposition of InP and related compounds. J. Electron. Mater. 12, 371–395 (1983). https://doi.org/10.1007/BF02651138-- March 1, 1983 ...[Visit Journal] The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga0.47In0.53 As and GaxIn1-xAsyP1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm2 V−1S−1 at 300 K and 58 900 cm2 V−1 S−1 at 772K, and for GaInAs was 11900 cm2 V−1 S−1 at 300 K, 54 600 cm2 V−1 S−1 at 77 K and 90 000 cm V−1S−1 at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current. [reprint (PDF)]
6.	Transport and photodetection in self-assembled semiconductor quantum dots M Razeghi, H Lim, S Tsao, J Szafraniec, W Zhang, K Mi and B Movaghar Nanotechnology 16 219-- January 7, 2005 ...[Visit Journal] A great step forward in science and technology was made when it was discovered that lattice mismatch can be used to grow highly ordered, artificial atom-like structures called self-assembled quantum dots. Several groups have in the meantime successfully demonstrated useful infrared photodetection devices which are based on this technology. The new physics is fascinating, and there is no doubt that many new applications will be found when we have developed a better understanding of the underlying physical processes, and in particular when we have learned how to integrate the exciting new developments made in nanoscopic addressing and molecular self-assembly methods with semiconducting dots. In this paper we examine the scientific and technical questions encountered in current state of the art infrared detector technology and suggest ways of overcoming these difficulties. Promoting simple physical pictures, we focus in particular on the problem of high temperature detector operation and discuss the origin of dark current, noise, and photoresponse. [reprint (PDF)]
6.	Breakthroughs Bring THz Spectroscopy, Sensing Closer to Mainstream Manijeh Razeghi, Quanyong Lu, Santanu Manna, Donghai Wu & Steven Slivken Photnics Spectra, December Issue, pp. 48-- December 1, 2016 ...[Visit Journal] The terahertz (THz) electromagnetic spectrum (1 to 10 THz), sitting between the infrared wavelengths on the higher frequency side and microwaves on the lower frequency side, lies unique and important properties. THz waves can pass through a number of materials, including synthetics, textiles, paper and cardboard. Many biomolecules, proteins, explosives or narcotics feature characteristic absorption I ines - so-called spectral "fingerprints" - at frequencies between 1 and 10 THz.
6.	Type-II superlattice photodetectors for MWIR to VLWIR focal plane arrays M. Razeghi, Y. Wei, A. Hood, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E. Michel and R. McClintock SPIE Infrared Technology and Applications Conference, April 17-21, 2006, Orlando, FL Proceedings – Infrared Technology and Applications XXXII, Vol. 6206, p. 62060N-1-- April 21, 2006 ...[Visit Journal] Results obtained on GaSb/InAs Type-II superlattices have shown performance comparable to HgCdTe detectors, with the promise of higher performance due to reduced Auger recombination and dark current through improvements in device design and material quality. In this paper, we discuss advancements in Type-II IR sensors that cover the 3 to > 30 µm wavelength range. Specific topics covered will be device design and modeling using the Empirical Tight Binding Method (ETBM), material growth and characterization, device fabrication and testing, as well as focal plane array processing and imaging. Imaging has been demonstrated at room temperature for the first time with a 5 µm cutoff wavelength 256×256 focal plane array. [reprint (PDF)]
6.	Quantum Hall effect in In0.53Ga0.47As-InP heterojunctions with two populated electric subbands Y. Guldner, J. P. Vieren, and M. Voos F. Delahaye and D. Dominguez J. P. Hirtz and M. Razeghi Phys. Rev. B 33, 3990 1986-- March 15, 1986 ...[Visit Journal] Quantum-Hall-effect and Shubnikov–de Haas measurements are presented for InxGa1−xAs?(hyInP heterojunctions with two populated electric subbands and low electron density (𝑛𝑠≤5×1011 cm−2). The Shubnikov–de Haas oscillations clearly show two different periodicities. An anomalous behavior of the quantum Hall effect is observed, in particular some plateaus are missing and other plateaus are enhanced. Precise measurements of the Hall resistance have been performed and it is shown that the resistance of the i=2 plateau is equal to its theoretical value h/2𝑒2 with an uncertainty of ∼10−8. [reprint (PDF)]
5.	Al_xGa_1-xN for Solar-Blind UV Detectors P. Sandvik, K. Mi, F. Shahedipour, R. McClintock, A. Yasan, P. Kung, and M. Razeghi Journal of Crystal Growth 231 (2001)-- January 1, 2001 ...[Visit Journal] We report on the metalorganic chemical vapor deposition of high quality AlGaN thin films on sapphire substrates over a wide range of Al concentrations. The quality of these AlGaN materials was verified through a demonstration of high performance visible and solar-blind UV p–i–n photodiodes with peak cutoff wavelengths ranging from 227 to 364 nm. External quantum efficiencies for these devices reached as high as 69% with over five orders rejection ratio from the peak to visible wavelengths. [reprint (PDF)]
5.	Quantum cascade laser: A tool for trace chemical detection Allan J. Evans; Manijeh Razeghi American Filtration and Separations Society - 20th Annual Conference and Exposition of the American Filtration and Separations Society 2:914-923 (2007)-- March 26, 2007 Laser-based trace chemical sensors are highly desired to enhance pollution filtering, health and safety monitoring, and filter efficiency monitoring for industrial processes. Limitations of current monitoring and sensing techniques are discussed and the benefits of mid-infrared spectroscopy using novel Quantum Cascade semiconductor Lasers (QCLs) are presented. These new techniques promise inexpensive, miniaturized sensors, capable of remote detection of trace chemicals in liquids, solids, and gasses with levels less than 1 part-per-billion. Applications of these techniques are discussed and the most recent developments of application-ready high power (> 100 mW), continuous-wave, mid-infrared QCLs operating above room temperature with lifetimes exceeding 12,000 hours are presented.
5.	-- November 30, 1999
5.	Midinfrared Semiconductor Photonics – A Roadmap:Quantum Cascade Lasers MANIJEH RAZEGHI arXiv:2511.03868 [physics.optics] ...[Visit Journal] Mid-wave infrared (IR) quantum cascade lasers (QCLs) offer high output power, excellent efficiency, broad wavelength tunability, and elevated operating temperatures, especially when operating in the 3–12 μm wavelength range. These characteristics make them highly promising for a wide range of applications, including high-resolution molecular spectroscopy, ultra-low-loss optical fiber communications using fluoride-based glasses (with attenuation below 2.5×10⁻⁴ dB/km), trace gas detection, air pollution monitoring (as many molecules, particularly hydrocarbons, exhibiting strong absorption lines in this spectral region), and medical diagnostics. This article presents a comprehensive overview of the development of QCLs, highlighting key milestones, the current state of the technology, and future directions, framed within the broader context of the Semiconductor Mid-Infrared Photonics Roadmap.
5.	Temperature dependence of the quantized Hall effect H. P. Wei, A. M. Chang, and D. C. Tsui M. Razeghi Phys. Rev. B 32, 7016(R) 1985-- November 15, 1985 ...[Visit Journal] We reported detailed measurements of the temperature dependence of the quantized Hall effect from 4.2 to 50 K in the i=2 plateau region in InGaAs-InP. We deduce from the data that there is a significant density of localized states between the two Landau levels, with a value of ∼1×1010 cm−2 meV−1 at the middle of the mobility gap. We also found that the correlations between 𝜎xx and 𝜎xy show the trend predicted by the recent two-parameter scaling theory of localization in quantized Hall effect. [reprint (PDF)]
5.	-- November 30, 1999
4.	Modeling the electronic band-structure of strained long-wavelength Type-II superlattices using the scattering matrix method Abbas Haddadi，Gail Brown，Manijeh Razeghi Abbas Haddadi,Brown Gail and Razeghi Manijeh.Modeling the electronic band-structure of strained long-wavelength Type-II superlattices using the scattering matrix method[J].Journal of Infrared and Millimeter Waves,2025,44(3):345~350 ...[Visit Journal] This study introduces a comprehensive theoretical framework for accurately calculating the electronic band-structure of strained long-wavelength InAs/GaSb type-II superlattices. Utilizing an eight-band k ⋅ p Hamilto⁃ nian in conjunction with a scattering matrix method， the model effectively incorporates quantum confinement， strain effects， and interface states. This robust and numerically stable approach achieves exceptional agreement with experimental data， offering a reliable tool for analyzing and engineering the band structure of complex multi⁃ layer systems
4.	An accurate method to check chemical interfaces of epitaxial III‐V compounds R. Bisaro; G. Laurencin; A. Friederich; M. Razeghi R. Bisaro, G. Laurencin, A. Friederich, M. Razeghi; An accurate method to check chemical interfaces of epitaxial III‐V compounds. Appl. Phys. Lett. 1 June 1982; 40 (11): 978–980.-- June 1, 1982 ...[Visit Journal] We have developed a method of chemical beveling coupled with line scan Auger measurements to check abrupt interfaces of epitaxial III‐V compounds. Interface widths between 53 and 89 Å have been measured by this method for an InP/Ga0.47In0.53As/InP double heterostructure grown by low pressure metalorganic chemical vapor deposition. The ultimate width checkable by this method lies between 10 and 15 Å and is of the order of magnitude of the escape depth of the Auger electrons selected.
4.	Unleashing light: a deep dive into quantum cascade laser dynamics through power, precision, and performance Xiaohan Yu, Yanbo Bai, Feihu Wang, Steve Slivken, Nirajman Shrestha, Ruiming Zhang, Nil Ozcevik, Manijeh Razeghi Xiaohan Yu, Yanbo Bai, Feihu Wang, Steve Slivken, Nirajman Shrestha, Ruiming Zhang, Nil Ozcevik, and Manijeh Razeghi "Unleashing light: a deep dive into quantum cascade laser dynamics through power, precision, and performance", Proc. SPIE 13908, Quantum Sensing and Nano Electronics and Photonics XXII, 139080U (20 March 2026); https://doi.org/10.1117/12.3082051 ...[Visit Journal] In this study, we explore the complex interplay of structural design and performance metrics in InGaAs/InAlAs/InP ridge waveguide quantum cascade lasers (QCLs) by combining theoretical modeling with rigorous experimental validation. By assuming mirror loss corresponding to a facet reflectivity of R = 0.275, which represents the Fresnel reflectance of uncoated InP facets, we investigated the impact of cavity length on threshold current density and slope efficiency by analyzing Power–Current–Voltage (PIV) characteristics of uncoated QCLs with lengths of 3mm, 4mm, and 5mm. Slope efficiencies were extracted and corrected for single-facet detection. By leveraging fitting techniques across multiple datasets and laser structure, we quantified internal and external quantum efficiencies and determined the transparency current density using graphical and analytical methods. A linear regression of inverse external efficiency versus inverse mirror loss enabled estimation of the internal quantum efficiency, highlighting the direct influence of fabrication parameters on laser output. With a linear fit of threshold current density versus mirror loss, the transparency current density was calculated. This work not only reinforces foundational laser physics principles but also provides a hands-on methodology for analyzing active device parameters with practical implications in tunable mid-infrared sources, spectroscopy, and optical sensing. [reprint (PDF)]
4.	Engineering of the fermi level in PLD-grown NiO thin films by post-annealing D. Rogers*, E. Sandana, M. Chamberlin, F. Teherani; V. Safarov, M. Konczykowski, R. Grasset, A. Alessi, H. Drouhin ; M. Razeghi We investigate practical routes to engineer the Fermi level—and thus the effective work function—of p-type nickel oxide (NiO) thin films grown on c-sapphire by plasma-assisted pulsed laser deposition (PA-PLD) at room temperature (RT). We examine three levers: (i) oxygen-rich growth at low substrate temperature, (ii) post-deposition annealing in air or oxygen across 320–620 °C, and (iii) impurity (Li) acceptor doping. RT-grown NiO exhibits high crystalline quality with (111) out-of-plane orientation, narrow rocking-curve width, and a film thickness near 60 nm. RT epitaxy yields the lowest resistivity among the studied conditions, and resistance increases progressively with temperature for iso-chronic post-annealing in air. Oxygen ambient post-annealing shows no distinctive monotonic trend in resistivity, although the conductivity falls off for annealing over about 500°C. Optical transmission spectra suggest progressive healing of in-gap defect states with post-annealing temperature. Doping NiO with 20at% of Li lowers resistivity relative to undoped NiO by an order of magnitude. Post-annealing at 300°C under oxygen ambient significantly boosts conductivity. Over a decade of storage, all films exhibited significant loss of conductivity, underscoring the need for stabilisation strategies. The results map practical processing windows to tune the NiO Fermi level for integration in oxide heterojunctions (e.g., p-NiO/n-Ga2O3) used in ultraviolet detection and wide-bandgap electronics.
4.	Quantum Devices Based on Modern Band Structure Engineering and Epitaxial Technology M. Razeghi Modern Physics Letters B, Vol. 22, No. 24, p. 2343-2371-- September 20, 2008 ...[Visit Journal] Modern band structure engineering is based both on the important discoveries of the past century and modern epitaxial technology. The general goal is to control the behavior of charge carriers on an atomic scale, which affects how they interact with each other and their environment. Starting from the basic semiconductor heterostructure, band structure engineering has evolved into a powerful discipline, employing lower dimensionality to demonstrate new material properties. Several modern technologies under development are used as examples of how this discipline is enabling new types of devices and new functionality in areas with immediate application.
4.	-- November 30, 1999
4.	SOLID-STATE DEEP UV EMITTERS/DETECTORS: Zinc oxide moves further into the ultraviolet David J. Rogers; Philippe Bove; Eric V. Sandana; Ferechteh Hosseini Teherani; Ryan McClintock; Manijeh Razeghi Laser Focus World. 2013;49(10):33-36.-- October 10, 2013 ...[Visit Journal] Latest advancements in the alloying of zinc oxide (ZnO) with magnesium (Mg) can offer an alternative to (Al) GaN-based emitters/detectors in the deep UV with reduced lattice and efficiency issues. The emerging potential of ZnO for UV emitter and detector applications is the result of a long, concerted, and fruitful R&D effort that has led to more than 7000 publications in 2012. ZnO is considered to be a potentially superior material for use in LEDs and laser diodes due to its larger exciton binding energy, as compared with 21 meV for GaN. Wet etching is also possible for ZnO with nearly all dilute acids and alkalis, while GaN requires hydrofluoric (HF) acid or plasma etching. High-quality ZnO films can be grown more readily on mismatched substrates and bulk ZnO substrates have better availability than their GaN equivalents.

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