Center for Quantum Devices - Most Downloaded Journal Articles

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378.	-- November 30, 1999
103.	nBn extended short-wavelength infrared focal plane array ARASH DEHZANGI, ABBAS HADDADI, ROMAIN CHEVALLIER, YIYUN ZHANG, AND MANIJEH RAZEGHI Optics Letters Vol. 43, Issue 3, pp. 591-594-- February 1, 2018 ...[Visit Journal] An extended short-wavelength nBn InAs/GaSb/AlSb type-II superlattice-based infrared focal plane array imager was demonstrated. A newly developed InAs_0.10Sb_0.90∕GaSb superlattice design was used as the large-bandgap electron barrier in this photodetector. The large band gap electron-barrier design in this nBn photodetector architecture leads to the device having lower dark current densities. A new bi-layer etch-stop scheme using a combination of InAs_0.91Sb_0.09 bulk and AlAs_0.1Sb_0.9∕GaSb superlattice layers was introduced to allow complete substrate removal and a shorter wavelength cut-on. Test pixels exhibit 100% cutoff wavelengths of ∼2.30 and ∼2.48 μm at 150 and 300 K, respectively. The devices achieve saturated quantum efficiency values of 59.7% and 63.8% at 150 and 300 K, respectively, under backside illumination and without any antireflection coating.At 150 K, photodetectors exhibit dark current density of 8.75 × 10⁻⁸ A∕cm² under −400 mV applied bias, providing specific detectivity of 2.82 × 10¹² cm · Hz^1∕2∕W at 1.78 μm. At 300 K, the dark current density reaches 4.75 × 10⁻² A∕cm² under −200 mV bias, providing a specific detectivity of 8.55 × 10⁹ cm · Hz^1∕2∕W 1.78 μm. [reprint (PDF)]
75.	Band-structure-engineered high-gain LWIR photodetector based on a type-II superlattice Arash Dehzangi, Jiakai Li and Manijeh Razeghi Light: Science & Applications volume 10, Article number: 17 (2021) https://doi.org/10.1038/s41377-020-00453-x ...[Visit Journal] The LWIR and longer wavelength regions are of particular interest for new developments and new approaches to realizing long-wavelength infrared (LWIR) photodetectors with high detectivity and high responsivity. These photodetectors are highly desirable for applications such as infrared earth science and astronomy, remote sensing, optical communication, and thermal and medical imaging. Here, we report the design, growth, and characterization of a high-gain band-structure-engineered LWIR heterojunction phototransistor based on type-II superlattices. The 1/e cut-off wavelength of the device is 8.0 µm. At 77 K, unity optical gain occurs at a 90 mV applied bias with a dark current density of 3.2 × 10−7 A/cm2. The optical gain of the device at 77 K saturates at a value of 276 at an applied bias of 220 mV. This saturation corresponds to a responsivity of 1284 A/W and a specific detectivity of 2.34 × 1013 cm Hz1/2/W at a peak detection wavelength of ~6.8 µm. The type-II superlattice-based high-gain LWIR device shows the possibility of designing the high-performance gain-based LWIR photodetectors by implementing the band structure engineering approach. [reprint (PDF)]
51.	Self-Detecting Mid-Infrared Dual-Comb Spectroscopy Based on High-Speed Injection-Locked Quantum Cascade Lasers Yu Ma, Dapeng Wu, Ruixin Huang, Shichen Zhang, Binru Zhou, Zejun Ma, Yongqiang Sun, Junqi Liu, Ning Zhuo, Jinchuan Zhang, Shenqiang Zhai, Shuman Liu, Fengqi Liu, Manijeh Razeghi, and Quanyong Lu Ma, Y., Wu, D., Huang, R., Zhang, S., Zhou, B., Ma, Z., Sun, Y., Liu, J., Zhuo, N., Zhang, J., Zhai, S., Liu, S., Liu, F., Razeghi, M. and Lu, Q. (2025), Self-Detecting Mid-Infrared Dual-Comb Spectroscopy Based on High-Speed Injection-Locked Quantum Cascade Lasers. Adv. Photonics Res. 2500062. https://doi.org/10.1002/adpr.202500062 ...[Visit Journal] Dual-comb spectrometer based on quantum cascade lasers (QCLs) is gaining fast development and revolutionizing the precision measurement with high-frequency and temporal resolutions. In these measurements, high-bandwidth photodetectors are normally used for signal acquisition and processing, which complicates the measurement system. QCL is well-known for its picosecond gain-recovery time with an intrinsic bandwidth of tens of GHz. In this work, a compact self-detecting dual-comb spectroscopy (DCS) is demonstrated based on dispersion-engineered, high-speed packaged QCLs under coherent injection locking. The laser source is designed and fabricated into a hybrid-monolithic-integrated waveguide and epi-down packaged on a wideband-designed submount to fully explore the high-speed feature up to fourth-order harmonic state with a cutoff frequency of 40 GHz. The effective radio frequency (RF) injection locking diminishes the issue of optical feedback and enables high-bandwidth self-detection based on QCLs. Clear and stable multiheterodyne signal corresponding to a spectral range of 68 cm−1 and narrow comb tooth linewidth of ≈10 kHz is observed without using external detector or numerical process. The demonstrated broadband, high-power, self-detecting mid-infrared QCL DCS has a great potential for future applications of molecular sensing and spectroscopy. [reprint (PDF)]
31.	-- November 30, 1999
27.	Ultrafast Pulse Generation from Quantum Cascade Lasers Feihu Wang, Xiaoqiong Qi, Zhichao Chen, Manijeh Razeghi, and Sukhdeep Dhillon Wang, F.; Qi, X.; Chen, Z.; Razeghi, M.; Dhillon, S. Ultrafast Pulse Generation from Quantum Cascade Lasers. Micromachines 2022, 13, 2063. https://doi.org/10.3390/ mi13122063 ...[Visit Journal] Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful to study ultrafast processes in MIR and THz using the targeted wavelength-by-design properties of QCLs. Since the first demonstration in 2009, mode-locking of QCLs has undergone considerable development in the past decade, which includes revealing the underlying mechanism of pulse formation, the development of an ultrafast THz detection technique, and the invention of novel pulse compression technology, etc. Here, we review the history and recent progress of ultrafast pulse generation from QCLs in both the THz and MIR regimes. [reprint (PDF)]
15.	High-power, high-wall-plug-efficiency quantum cascade lasers with high-brightness in continuous wave operation at 3–300μm Manijeh Razeghi, Yanbo Bai and Feihu Wang Razeghi et al. Light: Science & Applications (2025) 14:252 ...[Visit Journal] Quantum cascade lasers (QCLs) are unipolar quantum devices based on inter-sub-band transitions. They break the electron-hole recombination mechanism in traditional semiconductor lasers, overcome the long-lasting bottleneck which is that the emission wavelength of semiconductor laser is completely dependent on the bandgap of semiconductor materials. Therefore, their emission wavelength is able to cover the mid-infrared (mid-IR) range and the “Terahertz gap” that is previously inaccessible by any other semiconductor lasers. [reprint (PDF)]
15.	High Performance Planar Antimony-Based Superlattice Photodetectors Using Zinc Diffusion Grown by MBE Jiakai Li, R. K. Saroj, Steven Slivken, V. H. Nguyen, Gail Brown and Manijeh Razeghi Photonics 2022, 9, 664 ...[Visit Journal] In this letter, we report a mid-wavelength infrared (MWIR) planar photodetector based on InAs/InAsSb type-II superlattices (T2SLs) that has a cut-off wavelength of 4.3 um at 77 K. The superlattice for the device was grown by molecular beam epitaxy while the planar device structure was achieved by Zinc diffusion process in a metal–organic chemical vapor deposition reactor. At 77 K, the peak responsivity and the corresponding quantum efficiency had the value of 1.42 A/W and 48% respectively at 3.7 um under -20 mV for the MWIR planar photodetector. At 77 K, the MWIR planar photodetector exhibits a dark current density of 2.0E5 A/cm^2 and the R0A value of ~3.0E2 Ohm cm^2 under -20 mV, which yielded a specific detectivity of 4.0E11 cm Hz^(1/2)/W at 3.7 um. At 150 K, the planar device showed a dark current density of 6.4E-5 A/cm^2 and a quantum efficiency of 49% at ~3.7 um under -20 mV, which yielded a specific detectivity of 2.0E11 cm Hz^(1/2)/W. [reprint (PDF)]
10.	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)]
10.	Combined resonant tunneling and rate equation modeling of terahertz quantum cascade lasers Zhichao Chen , Andong Liu, Dong Chang , Sukhdeep Dhillon , Manijeh Razeghi , Feihu Wang Journal of Applied Physics, 135, 115703 ...[Visit Journal] Terahertz (THz) quantum cascade lasers (QCLs) are technologically important laser sources for the THz range but are complex to model. An efficient extended rate equation model is developed here by incorporating the resonant tunneling mechanism from the density matrix formalism, which permits to simulate THz QCLs with thick carrier injection barriers within the semi-classical formalism. A self-consistent solution is obtained by iteratively solving the Schrödinger-Poisson equation with this transport model. Carrier-light coupling is also included to simulate the current behavior arising from stimulated emission. As a quasi-ab initio model, intermediate parameters such as pure dephasing time and optical linewidth are dynamically calculated in the convergence process, and the only fitting parameters are the interface roughness correlation length and height. Good agreement has been achieved by comparing the simulation results of various designs with experiments, and other models such as density matrix Monte Carlo and non-equilibrium Green’s function method that, unlike here, require important computational resources. The accuracy, compatibility, and computational efficiency of our model enables many application scenarios, such as design optimization and quantitative insights into THz QCLs. Finally, the source code of the model is also provided in the supplementary material of this article for readers to repeat the results presented here, investigate and optimize new designs. [reprint (PDF)]
9.	Development of high power, InP-based quantum cascade lasers on alternative epitaxial platforms Steven Slivken, Nirajman Shrestha, Manijeh Razeghi Proc. of SPIE Vol. 12895, Quantum Sensing and Nano Electronics and Photonics XX, 1289503 (28 January - 1 February 2024, San Francisco) doi: 10.1117/12.3009335 ...[Visit Journal] In this talk, challenges and solutions associated with the monolithic, epitaxial integration of mid- and longwave- infrared, InP-based quantum cascade lasers on GaAs and Si wafers will be discussed. Initial results, including room temperature, high power, and continuous wave operation, will be described. [reprint (PDF)]
8.	High-brightness LWIR quantum cascade lasers F. Wang, S. Slivken, and M. Razeghi F. Wang, S. Slivken, and M. Razeghi, High-brightness LWIR quantum cascade lasers, Optics Letters, vol. 46, No. 20, 5193 ...[Visit Journal] Long-wave infrared (LWIR, lambda~8-12 um) quantum cascade lasers (QCLs) are drawing increasing interest, as they provide the possibility of long-distance transmission of light through the atmosphere owing to the reduced water absorption. However, their development has been lagging behind the shorter wavelength QCLs due to much bigger technological challenges. In this Letter, through band structure engineering based on a highly localized diagonal laser transition strategy and out-coupler design using an electrically isolated taper structure, we demonstrate high beam quality single-mode LWIR QCLs with high-brightness (2.0 MW cm^-2 sr^-1 for lambda~10 um, 2.2 MW cm^-2 sr^-1 for lambda~9 um, 5.0 MW cm^-2 sr^-1 for lambda~8 um) light extraction from a single facet in continuous-wave operation at 15 ^oC. These results mark an important milestone in exploring the lighting capability of inter-sub-band semiconductor lasers in the LWIR spectral range. [reprint (PDF)]
8.	Photovoltaic MWIR type-II superlattice focal plane array on GaAs substrate E.K. Huang, P.Y. Delaunay, B.M. Nguyen, S. Abdoullahi-Pour, and M. Razeghi IEEE Journal of Quantum Electronics (JQE), Vol. 46, No. 12, p. 1704-1708-- December 1, 2010 ...[Visit Journal] Recent improvements in the performance of Type-II superlattice (T2SL) photodetectors has spurred interest in developing low cost and large format focal plane arrays (FPA) on this material system. Due to the limitations of size and cost of native GaSb substrates, GaAs is an attractive alternative with 8” wafers commercially available, but is 7.8% lattice mismatched to T2SL. In this paper, we present a photovoltaic T2SL 320 x 256 focal plane array (FPA) in the MWIR on GaAs substrate. The FPA attained a median noise equivalent temperature difference (NEDT) of 13 mK and 10mK (F#=2.3) with integration times of 10.02 ms and 19.06 ms respectively at 67 K. [reprint (PDF)]
7.	Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD Manijeh Razeghi, Junhee Lee, Lakshay Gautam, Jean-Pierre Leburton, Ferechteh H. Teherani, Pedram Khalili Amiri, Vinayak P. Dravid and Dimitris Pavlidis Photonics 2021, 8(12), 578; ...[Visit Journal] Gallium oxide (Ga2O3) thin films of various thicknesses were grown on sapphire (0001) substrates by metal organic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa), high purity deionized water, and silane (SiH4) as gallium, oxygen, and silicon precursors, respectively. N2 was used as carrier gas. Hall measurements revealed that films grown with a lower VI/III ratio had a dominant p-type conduction with room temperature mobilities up to 7 cm2/Vs and carrier concentrations up to ~1020 cm−3 for thinner layers. High resolution transmission electron microscopy suggested that the layers were mainly κ phase. Microstrip field-effect transistors (FETs) were fabricated using 2D p-type Ga2O3:Si, channels. They achieved a maximum drain current of 2.19 mA and an on/off ratio as high as ~108. A phenomenological model for the p-type conduction was also presented. As the first demonstration of a p-type Ga2O3, this work represents a significant advance which is state of the art, which would allow the fabrication of p-n junction based devices which could be smaller/thinner and bring both cost (more devices/wafer and less growth time) and operating speed (due to miniaturization) advantages. Moreover, the first scaling down to 2D device channels opens the prospect of faster devices and improved heat evacuation [reprint (PDF)]
7.	High Performance InAs/InAsSb Type-II Superlattice Mid-Wavelength Infrared Photodetectors with Double Barrier Donghai Wu, Jiakai Li, Arash Dehzangi, Manijeh Razeghi Infrared Physics &Technology 103439-- July 18, 2020 ...[Visit Journal] By introducing a double barrier design, a high performance InAs/InAsSb type-II superlattice mid-wavelength infrared photodetector has been demonstrated. The photodetector exhibits a cut-off wavelength of ~4.50 µm at 150 K. At 150 K and −120 mV applied bias, the photodetector exhibits a dark current density of 1.21 × 10−5 A/cm2, a quantum efficiency of 45% at peak responsivity (~3.95 µm), and a specific detectivity of 6.9 × 1011 cm·Hz1/2/W. The photodetector shows background-limited operating temperature up to 160 K. [reprint (PDF)]
7.	Room Temperature Terahertz and Frequency Combs Based on Intersubband Quantum Cascade Laser Diodes: History and Future e Manijeh Razeghi , and Quanyong Lu Manijeh Razeghi, and Quanyong Lu Room Temperature Terahertz and Frequency Combs Based on Intersubband Quantum Cascade Laser Diodes: History and Futur Photonics 2025, 12(1), 79; ...[Visit Journal] : The year 2024 marks the 30-year anniversary of the quantum cascade laser (QCL), which is becoming the leading laser source in the mid-infrared (mid-IR) range. Since the first demonstration, QCL has undergone tremendous development in terms of the output power, wall plug efficiency, spectral coverage, wavelength tunability, and beam quality. Owing to its unique intersubband transition and fast gain features, QCL possesses strong nonlinearities that makes it an ideal platform for nonlinear photonics like terahertz (THz) difference frequency generation and direct frequency comb generation via fourwave mixing when group velocity dispersion is engineered. The feature of broadband, high-power, and low-phase noise of QCL combs is revolutionizing mid-IR spectroscopy and sensing by offering a new tool measuring multi-channel molecules simultaneously in the µs time scale. While THz QCL difference frequency generation is becoming the only semiconductor light source covering 1–5 THz at room temperature. In this paper, we will introduce the latest research from the Center for Quantum Devices at Northwestern University and briefly discuss the history of QCL, recent progress, and future perspective of QCL research, especially for QCL frequency combs, room temperature THz QCL difference frequency generation, and major challenges facing QCL in the future. [reprint (PDF)]
7.	Quantum cascade lasers that emit more light than heat Y. Bai, S. Slivken, S. Kuboya, S.R. Darvish and M. Razeghi Nature Photonics, February 2010, Vol. 4, p. 99-102-- February 1, 2010 ...[Visit Journal] For any semiconductor lasers, the wall plug efficiency, that is, the portion of the injected electrical energy that can be converted into output optical energy, is one of the most important figures of merit. A device with a higher wall plug efficiency has a lower power demand and prolonged device lifetime due to its reduced self-heating. Since its invention, the power performance of the quantum cascade laser has improved tremendously. However, although the internal quantum efficiency can be engineered to be greater than 80% at low temperatures, the wall plug efficiency of a quantum cascade laser has never been demonstrated above 50% at any temperature. The best wall plug efficiency reported to date is 36% at 120 K. Here, we overcome the limiting factors using a single-well injector design and demonstrate 53% wall plug efficiency at 40 K with an emitting wavelength of 5 µm. In other words, we demonstrate a quantum cascade laser that produces more light than heat. [reprint (PDF)]
7.	Comparison of PLD-Grown p-NiO/n-Ga2O3 Heterojunctions on Bulk Single Crystal β-Ga2O3 and r-plane Sapphire Substrates D. J. Rogers , V. E. Sandana, F. Hosseini Teherani and M. Razeghi Proc. of SPIE Vol. 12895, Quantum Sensing and Nano Electronics and Photonics XX, 128870J (28 January - 1 February 2024 San Francisco)doi: 10.1117/12.3012511 ...[Visit Journal] p-NiO/n-Ga2O3 heterostructures were formed on single crystal (-201) β (monoclinic) Ga2O3 and r-sapphire substrates by Pulsed Laser Deposition. Ring mesa layer stacks were created using a shadow mask during growth. X-Ray diffraction studies were consistent with the formation of (111) oriented fcc NiO on the bulk Ga2O3 and randomly oriented fcc NiO on (102) oriented β-Ga2O3 /r-sapphire. RT optical transmission studies revealed bandgap energy values of ~3.65 eV and ~5.28 eV for the NiO and Ga2O3 on r-sapphire. p-n junction devices were formed by depositing gold contacts on the layer stacks using shadow masks in a thermal evaporator. Both heterojunctions showed rectifying I/V characteristics. On bulk Ga2O, the junction showed a current density over 16mA/cm2 at +20V forward bias and a reverse bias leakage current over 3 orders of magnitude lower at -20V (1 pA). On Ga2O3/r-sapphire the forward bias current density at +15V was about an order of magnitude lower than for the p-NiO/bulk n-Ga2O3 heterojunction while the reverse bias leakage current at -15V (~ 20 pA) was an order of magnitude higher. Hence the NiO/bulk Ga2O3 junction was more rectifying. Upon illumination with a Xenon lamp a distinct increase in current was observed for the IV curves in both devices (four orders of magnitude for -15V reverse bias in the case of the p-NiO/bulk n-Ga2O3 heterojunction). The p-NiO/n-Ga2O3/rsapphire junction gave a spectral responsivity with a FWHM value of 80nm and two distinct response peaks (with maxima at 230 and 270nm) which were attributed to carriers being photogenerated in the Ga2O3 underlayer. For both devices time response studies showed a 10%/90% rise and fall of the photo generated current upon shutter open and closing which was relatively abrupt (millisecond range), and there was no evidence of significant persistent photoconductivity. [reprint (PDF)]
6.	Mid-wavelength infrared heterojunction phototransistors based on type-II InAs/AlSb/GaSb superlattices A. Haddadi, S. Adhikary, A. Dehzangi, and M. Razeghi Applied Physics Letters 109, 021107-- July 12, 2016 ...[Visit Journal] A mid-wavelength infrared heterojunction phototransistor based on type-II InAs/AlSb/GaSb superlattices on GaSb substrate has been demonstrated. Near a wavelength of 4 μm saturated optical gains of 668 and 639 at 77 and 150 K, respectively, are demonstrated over a wide dynamic range. At 150 K, the unity optical gain collector dark current density and DC current gain are 1 × 10⁻³ A/cm² and 3710, respectively. This demonstrates the potential for use in high-speed applications. In addition, the phototransistor exhibits a specific detectivity value that is four times higher compared with a state-of-the-art type-II superlattice-based photodiode with a similar cut-off wavelength at 150 K. [reprint (PDF)]
6.	III-Nitride Optoelectronic Devices: From Ultraviolet Toward Terahertz M. Razeghi IEEE Photonics Journal-Breakthroughs in Photonics 2010, Vol. 3, No. 2, p. 263-267-- April 26, 2011 ...[Visit Journal] We review III-Nitride optoelectronic device technologies with an emphasis on recent breakthroughs. We start with a brief summary of historical accomplishments and then report the state-of-the-art in three key spectral regimes: (1) Ultraviolet (AlGaN-based avalanche photodiodes, single photon detectors, focal plane arrays, and light emitting diodes), (2) Visible (InGaN-based solid state lighting, lasers, and solar cells), and (3) Near-, mid-infrared, and terahertz (AlGaN/GaN-based gap-engineered intersubband devices). We also describe future trends in III-Nitride optoelectronic devices. [reprint (PDF)]
6.	Investigation of Enhanced Heteroepitaxy and Electrical Properties in k-Ga2O3 due to Interfacing with β-Ga2O3 Template Layers Junhee Lee, Lakshay Gautam, Ferechteh H. Teherani, Eric V. Sandana, P. Bove, David J. Rogers and Manijeh Razeghi J. Lee, M. Razeghi, Physica Status Solidi A 2023,220, 2200559, https://doi.org/10.1002/pssa.202200559 ...[Visit Journal] Heteroepitaxial k-Ga2O3 films grown by metal-organic chemical vapor deposition (MOCVD) were found to have superior materials and electrical properties thanks to the interfacing with a b-Ga2O3 template layer. k-Ga2O3grown on sapphire has not been able to demonstrate its full potential due to materials imperfections created by strain induced by the lattice mismatch at the interface between the epilayer and the substrate. By adopting a b-Ga2O3 template on a c-sapphire substrate, higher quality k-Ga2O3thin films were obtained, as evidenced by a smoother surface morphology, narrower XRD peaks, and superior electrical performance. The implications of this phenomenon, caused by b-Ga2O3 buffer layer, are already very encouraging for both boosting current device performance and opening up the perspective of novel applications for Ga2O3. [reprint (PDF)]
6.	Investigation of the factors influencing nanostructure array growth by PLD towards reproducible wafer-scale growth Vinod E. Sandana; David. J. Rogers; Ferechteh Hosseini Teherani; Philippe Bove; Manijeh Razeghi physica status solidi (a) Applications and Materials Science. Volume 211, Issue 2, pages 449–454, (February 2014)-- January 14, 2014 ...[Visit Journal] The growth of catalyst-free ZnO nanostructure arrays on silicon (111) substrates by pulsed laser deposition was investigated. Without an underlayer, randomly oriented, micron-scale structures were obtained. Introduction of a c-axis oriented ZnO underlayer resulted in denser arrays of vertically oriented nanostructures with either tapering, vertical-walled or broadening forms, depending on background Ar pressure. Nanostructure pitch seemed to be determined by underlayer grain size while nanostructure widths could be narrowed from ∼100–500 to ∼10–50 nm by a 50 °C increase in growth temperature. A dimpled underlayer topography correlated with the moth-eye type arrays while a more granular surface was linked to vertically walled nanocolumns. Between-wafer reproducibility was demonstrated for both moth-eye and vertical nanocolumn arrays. Broadening nanostructures proved difficult to replicate, however. Full 2 inch wafer coverage was obtained by rastering the target with the laser beam. [reprint (PDF)]
6.	Al_xGa_1−xN-based solar-blind ultraviolet photodetector based on lateral epitaxial overgrowth of AlN on Si substrate E. Cicek, R. McClintock, C. Y. Cho, B. Rahnema, and M. Razeghi Appl. Phys. Lett. 103, 181113 (2013)-- October 30, 2013 ...[Visit Journal] We report on Al_xGa_1−xN-based solar-blind ultraviolet (UV) photodetector (PD) grown on Si(111) substrate. First, Si(111) substrate is patterned, and then metalorganic chemical vapor deposition is implemented for a fully-coalesced ∼8.5 μm AlN template layer via a pulsed atomic layer epitaxial growth technique. A back-illuminated p-i-n PD structure is subsequently grown on the high quality AlN template layer. After processing and implementation of Si(111) substrate removal, the optical and electrical characteristic of PDs are studied. Solar-blind operation is observed throughout the array; at the peak detection wavelength of 290 nm, 625 μm² area PD showed unbiased peak external quantum efficiency and responsivity of ∼7% and 18.3 mA/W, respectively, with a UV and visible rejection ratio of more than three orders of magnitude. Electrical measurements yielded a low-dark current density below 1.6 × 10⁻⁸ A/cm² at 10 V reverse bias. [reprint (PDF)]
6.	Study of Phase Transition in MOCVD Grown Ga2O3 from κ to β Phase by Ex Situ and In Situ Annealing Junhee Lee, Honghyuk Kim, Lakshay Gautam, Kun He, Xiaobing Hu, Vinayak P. Dravid and Manijeh Razeghi Photonics 2021, 8, 17. https://doi.org/10.3390/ photonics8010017 ...[Visit Journal] We report the post-growth thermal annealing and the subsequent phase transition of Ga2O3 grown on c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). We demonstrated the post-growth thermal annealing at temperatures higher than 900 °C under N2 ambience, by either in situ or ex situ thermal annealing, can induce phase transition from nominally metastable κ- to thermodynamically stable β-phase. This was analyzed by structural characterizations such as high-resolution scanning transmission electron microscopy and x-ray diffraction. The highly resistive as-grown Ga2O3 epitaxial layer becomes conductive after annealing at 1000 °C. Furthermore, we demonstrate that in situ annealing can lead to a crack-free β-Ga2O3. [reprint (PDF)]
6.	Continuous wave quantum cascade lasers with 5.6 W output power at room temperature and 41% wall-plug efficiency in cryogenic operation F. Wang, S. Slivken, D. H. Wu, Q. Y. Lu, and M. Razeghi AIP Advances 10, 055120-- May 19, 2020 ...[Visit Journal] In this paper, we report a post-polishing technique to achieve nearly complete surface planarization for the buried ridge regrowth processing of quantum cascade lasers. The planarized device geometry improves the thermal conduction and reliability and, most importantly, enhances the power and efficiency in continuous wave operation. With this technique, we demonstrate a high continuous wave wall-plug efficiency of an InP-based quantum cascade laser reaching ∼41% with an output power of ∼12 W from a single facet operating at liquid nitrogen temperature. At room temperature, the continuous wave output power exceeds the previous record, reaching ∼5.6 W. [reprint (PDF)]

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