Center for Quantum Devices - Most Downloaded Journal Articles

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15.	Kinetics of Quantum States in Quantum Cascade Lasers: Device Design Principles and fabrication M. Razeghi special issue of Microelectronics Journal 30 (10)-- October 1, 1999[reprint (PDF)]
15.	Monolithic terahertz source Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai and M. Razeghi Nature Photonics \| Research Highlights -- July 31, 2014 ...[Visit Journal] To date, the production of continuous-wave terahertz (THz) sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers operating at room temperature has proved elusive. A critical problem is that, to achieve a large nonlinear susceptibility for frequency conversion, the active region of the quantum cascade laser requires high doping, which elevates the lasing threshold current density. Now, Quan-Yong Lu and colleagues from Northwestern University in the USA have overcome this problem and demonstrated a room-temperature continuous-wave THz source based on difference-frequency generation in quantum cascade lasers. They designed quantum-well structures based on In_0.53Ga_0.47As/In_0.52Al_0.48As material system for two mid-infrared wavelengths. The average doping in the active region was about 2.5 × 10¹⁶ cm⁻³. A buried ridge, buried composite distributed-feedback waveguide with the Čerenkov phase-matching scheme was used to reduce the waveguide loss and enhance heat dissipation. As a result, single-mode emission at 3.6 THz was observed at 293 K. The continuous-wave THz power reached 3 μW with a conversion efficiency of 0.44 mW W⁻² from mid-infrared to THz waves. Using a similar device design, a THz peak power of 1.4 mW was achieved in pulse mode. [reprint (PDF)]
15.	Characterization of ZnO thin films grown on c-sapphire by pulsed laser deposition as templates for regrowth of zno by metal organic chemical vapor deposition D. J. Rogers ; F. Hosseini Teherani ; C. Sartel ; V. Sallet ; F. Jomard ; P. Galtier ; M. Razeghi Proc. SPIE 7217, Zinc Oxide Materials and Devices IV, 72170F (February 17, 2009)-- February 17, 2009 ...[Visit Journal] The use of ZnO template layers grown Pulsed Laser Deposition (PLD) has been seen to produce dramatic improvements in the surface morphology, crystallographic quality and optical properties of ZnO layers grown on c-sapphire substrates by Metal Organic Chemical Vapor Deposition. This paper provides complementary details on the PLD-grown ZnO template properties. [reprint (PDF)]
15.	High Power 280 nm AlGaN Light Emitting Diodes Based on an Asymmetric Single Quantum Well K. Mayes, A. Yasan, R. McClintock, D. Shiell, S.R. Darvish, P. Kung, and M. Razeghi Applied Physics Letters, 84 (7)-- February 16, 2004 ...[Visit Journal] We demonstrate high-power AlGaN-based ultraviolet light-emitting diodes grown on sapphire with an emission wavelength of 280 nm using an asymmetric single-quantum-well active layer configuration on top of a high-quality AlGaN/AlN template layer. An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 µm×300 µm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current. [reprint (PDF)]
15.	Gas-Source Molecular Beam Epitaxy Growth of 8.5 μm Quantum Cascade Laser S. Slivken, C. Jelen, A. Rybaltowski, J. Diaz and M. Razeghi Applied Physics Letters 71 (18)-- November 1, 1997 ...[Visit Journal] We demonstrate preliminary results for an 8.5 μm laser emission from quantum cascade lasers grown in a single step by gas-source molecular beam epitaxy. 70 mW peak power per two facets is recorded for all devices tested at 79 K with 1 μs pulses at 200 Hz. For a 3 mm cavity length, lasing persists up to 270 K with a T0 of 180 K. [reprint (PDF)]
15.	Aluminum gallium nitride short-period superlattices doped with magnesium A. Saxler, W.C. Mitchel, P. Kung and M. Razeghi Applied Physics Letters 74 (14)-- April 9, 1999 ...[Visit Journal] Short-period superlattices consisting of alternating layers of GaN:Mg and AlGaN:Mg were grown by low-pressure organometallic vapor phase epitaxy. The electrical properties of these superlattices were measured as a function of temperature and compared to conventional AlGaN:Mg layers. It is shown that the optical absorption edge can be shifted to shorter wavelengths while lowering the acceptor ionization energy by using short-period superlattice structures instead of bulk-like AlGaN:Mg. [reprint (PDF)]
15.	Continuous operation of a monolithic semiconductor terahertz source at room temperature Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai, and M. Razeghi Appl. Phys. Lett. 104, 221105 (2014)-- June 3, 2014 ...[Visit Journal] We demonstrate room temperature continuous wave THz sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers. Buried ridge, buried composite distributed-feedback waveguide with Čerenkov phase-matching scheme is used to reduce the waveguide loss and enhance the heat dissipation for continuous wave operation. Continuous emission at 3.6 THz with a side-mode suppression ratio of 20 dB and output power up to 3 μW are achieved, respectively. THz peak power is further scaled up to 1.4 mW in pulsed mode by increasing the mid-infrared power through increasing the active region doping and device area. [reprint (PDF)]
15.	High performance antimony based type-II superlattice photodiodes on GaAs substrates B.M. Nguyen, D. Hoffman, E.K. Huang, P.Y. Delaunay, and M. Razeghi SPIE Porceedings, Vol. 7298, Orlando, FL 2009, p. 72981T-- April 13, 2009 ...[Visit Journal] In recent years, Type-II InAs/GaSb superlattices grown on GaSb substrate have achieved significant advances in both structural design and material growth, making Type-II superlattice infrared detector a rival competitor to the state-of-the-art MCT technology. However, the limited size and strong infrared absorption of GaSb substrates prevent large format type-II superlattice infrared imagers from being realized. In this work, we demonstrate type-II superlattices grown on GaAs substrates, which is a significant step toward third generation infrared imaging at low cost. The device performances of Type-II superalttice photodetectors grown on these two substrates are compared. [reprint (PDF)]
15.	High performance Type-II InAs/GaSb superlattices for mid, long, and very long wavelength infrared focal plane arrays M. Razeghi, Y. Wei, A. Gin, A. Hood, V. Yazdanpanah, M.Z. Tidrow, and V. Nathan SPIE Conference, Orlando, FL, Vol. 5783, pp. 86-- March 28, 2005 ...[Visit Journal] We present our most recent results and review our progress over the past few years regarding InAs/GaSb Type-II superlattices for photovoltaic detectors and focal plane arrays. Empirical tight binding methods have been proven to be very effective and accurate in designing superlattices for various cutoff wavelengths from 3.7 µm up to 32 µm. Excellent agreement between theoretical calculations and experimental results has been obtained. High quality material growths were performed using an Intevac modular Gen II molecular beam epitaxy system. The material quality was characterized using x-ray, atomic force microscopy, transmission electron microscope and photoluminescence, etc. Detector performance confirmed high material electrical quality. Details of the demonstration of 256×256 long wavelength infrared focal plane arrays are presented. [reprint (PDF)]
15.	High Power, Continuous-Wave, Quantum Cascade Lasers for MWIR and LWIR Applications S. Slivken, A. Evans, J.S. Yu, S.R. Darvish and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 612703-- January 23, 2006 ...[Visit Journal] Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. Since 2002, the power levels for individual devices have jumped from 20 mW to 600 mW. Expanding on this development, we have able to demonstrate continuous wave operation at many wavelengths throughout the mid- and far-infrared spectral range, and have now achieved >100 mW output in the 4.0 to 9.5 µm range. [reprint (PDF)]
15.	Semiconductor ultraviolet detectors M. Razeghi and A. Rogalski SPIE Photonics West '96 Photodetectors: Materials and Devices; Proceedings 2685-- January 27, 1996 ...[Visit Journal] This paper presents an overview of semiconductor ultraviolet (UV) detectors that are currently available and associated technologies that are undergoing further development. At the beginning, the classification of UV detectors and general requirements imposed on these detectors are presented. Further consideration are restricted to modern semiconductor UV detectors, so the current state-of-the-art of different types of semiconductor UV detectors is presented. Hitherto, the semiconductor UV detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main effort are currently directed to a new generation of UV detectors fabricated from wide-band-gap semiconductors between them the most promising are diamond and AlGaN. The latest progress in development of AlGaN UV detectors is finally described in detail. [reprint (PDF)]
15.	Growth of InAsSb Alloys on GaAs and Si Substrates for Uncooled Infrared Photodetector Applications J.D. Kim, H. Mohseni, J.S. Wojkowski, J.J. Lee and M. Razeghi SPIE Conference, San Jose, CA, -- January 27, 1999 ...[Visit Journal] In this paper, we report on the growth and characterization of InAsSb alloys on GaAs and Si substrates for uncooled infrared photodetector applications. The fabrication and characterization of photodetectors from the grown layers are also reported. The photovoltaic and photoconductive devices were grown on (100) GaAs and Si substrates, respectively, using molecular beam epitaxy (MBE). The composition of InAs>sub>1-xSb_x layers was 0.95 in both cases and cut-off wavelength of 7-8 μm has been obtained. At 300 K, the photovoltaic detectors on GaAs substrates resulted in a sharp cut-off wavelength of 7.5 μm with a peak responsivity as high as 0.32 V/W at 6.5 micrometer. For the photoconductive detectors on Si substrates, cut-off wavelength of 8 μm has been observed with a responsivity of 6.3x10^-2 V/W at 7 μm under an electric field of 420 V/m. [reprint (PDF)]
15.	High performance monolithic, broadly tunable mid-infrared quantum cascade lasers WENJIA Zhou, DONGHAI Wu, RYAN McCLINTOCK, STEVEN SLIVKEN, AND MANIJEH RAZEGH1 Optica 4(10), p. 1228-- October 10, 2017 ...[Visit Journal] Mid-infrared lasers, emitting in the spectral region of 3-12 µm that contains strong characteristic vibrational transitions of many important molecules, are highly desirable for spectroscopy sensing applications. High-efficiency quantum cascade lasers have been demonstrated with up to watt-level output power in the mid-infrared region. However, the wide wavelength tuning that is critical for spectroscopy applications still largely relies on incorporating external gratings, which have stability issues. Here, we demonstrate a monolithic, broadly tunable quantum cascade laser source emitting between 6.1 and 9.2 µm through an on-chip integration of a sampled grating distributed feedback tunable laser array and a beam combiner. High peak power up to 65 mW has been obtained through a balanced high-gain active region design, efficient waveguide layout, and the development of a broadband antireflection coating. Nearly fundamental transversemode operation is achieved for all emission wavelengths with a pointing stability better than 1.6 mrad (0.1 °). The demonstrated laser source opens new opportunities for mid-infrared spectroscopy. [reprint (PDF)]
15.	Demonstration of high performance long wavelength infrared Type-II InAs/GaSb superlattice photodidoe grown on GaAs substrate S. Abdollahi Pour, B.M. Nguyen, S. Bogdanov, E.K. Huang, and M. Razeghi Applied Physics Letters, Vol. 95, No. 17, p. 173505-- October 26, 2009 ...[Visit Journal] We report the growth and characterization of long wavelength infrared type-II InAs/GaSb superlattice photodiodes with a 50% cut-off wavelength at 11 µm, on GaAs substrate. Despite a 7.3% lattice mismatch to the substrate, photodiodes passivated with polyimide exhibit an R₀A value of 35 Ω·cm² at 77 K, which is in the same order of magnitude as reference devices grown on native GaSb substrate. With a reverse applied bias less than 500 mV, the dark current density and differential resistance-area product are close to that of devices on GaSb substrate, within the tolerance of the processing and measurement. The quantum efficiency attains the expected value of 20% at zero bias, resulting in a Johnson limited detectivity of 1.1×10¹¹ Jones. Although some difference in performances is observed, devices grown on GaAs substrate already attained the background limit performance at 77 K with a 300 K background and a 2-π field of view. [reprint (PDF)]
15.	Low irradiance background limited type-II superlattice MWIR M-barrier imager E.K. Huang, S. Abdollahi Pour, M.A. Hoang, A. Haddadi, M. Razeghi and M.Z. Tidrow OSA Optics Letters (OL), Vol. 37, No. 11, p. 2025-2027-- June 1, 2012 ...[Visit Journal] We report a type-II superlattice mid-wave infrared 320 × 256 imager at 81 K with the M-barrier design that achieved background limited performance (BLIP) and ∼99%operability. The 280 K blackbody’s photon irradiance was limited by an aperture and a band-pass filter from 3.6 μm to 3.8 μm resulting in a total flux of ∼5 × 10¹² ph·cm⁻²·s⁻¹. Under these low-light conditions, and consequently the use of a 13.5 ms integration time, the imager was observed to be BLIP thanks to a ∼5 pA dark current from the 27 μm wide pixels. The total noise was dominated by the photon flux and read-out circuit which gave the imager a noise equivalent input of ∼5 × 10¹⁰ ph·cm⁻²·s⁻¹ and temperature sensitivity of 9 mK with F∕2.3 optics. Excellent imagery obtained using a 1-point correction alludes to the array’s uniform responsivity. [reprint (PDF)]
15.	Type-II superlattice-based extended short-wavelength infrared focal plane array with an AlAsSb/GaSb superlattice etch-stop layer to allow near-visible light detection Romain Chevallier, Arash Dehzangi, Abbas Haddadi, and Manijeh Razeghi Optics Letters Vol. 42, Iss. 21, pp. 4299-4302-- October 17, 2017 ...[Visit Journal] A versatile infrared imager capable of imaging the near-visible to the extended short-wavelength infrared (e-SWIR) is demonstrated using e-SWIR InAs/GaSb/AlSb type-II superlattice-based photodiodes. A bi-layer etch-stop scheme consisting of bulk InAs_0.91Sb_0.09 and AlAs_0.1Sb_0.9/GaSb superlattice layers is introduced for substrate removal from the hybridized back-side illuminated photodetectors. The implementation of this new technique on an e-SWIR focal plane array results in a significant enhancement in the external quantum efficiency (QE) in the 1.8–0.8μm spectral region, while maintaining a high QE at wavelengths longer than 1.8μm. Test pixels exhibit 100% cutoff wavelengths of ∼2.1 and ∼2.25μm at 150 and 300K, respectively. They achieve saturated QE values of 56% and 68% at 150 and 300K, respectively, under back-side illumination and without any anti-reflection coating. At 150K, the photodetectors (27μm×27μm area) exhibit a dark current density of 4.7×10⁻⁷ A/cm² under a −50 mV applied bias providing a specific detectivity of 1.77×10¹² cm·Hz^1/2/W. At 300K, the dark current density reaches 6.6×10⁻² A/cm² under −50 mV bias, providing a specific detectivity of 5.17×10⁹ cm·Hz^1/2/W. [reprint (PDF)]
15.	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)]
15.	Electroluminescence of InAs/GaSb heterodiodes D. Hoffman, A. Hood, E. Michel, F. Fuchs, and M. Razeghi IEEE Journal of Quantum Electronics, 42 (2)-- February 1, 2006 ...[Visit Journal] The electroluminescence of a Type-II InAs-GaSb superlattice heterodiode has been studied as a function of injection current and temperature in the spectral range between 3 and 13 μm. The heterodiode comprises a Be-doped midwavelength infrared (MWIR) superlattice with an effective bandgap around 270 meV and an undoped long wavelength infrared (LWIR) superlattice with an effective bandgap of 115 meV. [reprint (PDF)]
15.	Growth and Characterization of Type-II Non-Equilibrium Photovoltaic Detectors for Long Wavelength Infrared Range H. Mohseni, J. Wojkowski, A. Tahraoui, M. Razeghi, G. Brown and W. Mitche SPIE Conference, San Jose, CA, -- January 26, 2000 ...[Visit Journal] Growth and characterization of type-II detectors for mid-IR wavelength range is presented. The device has a p-i-n structure is designed to operate in the non-equilibrium mode with low tunneling current. The active layer is a short period InAs/GaSb superlattice. Wider bandgap p-type AlSb and n-type InAs layers are used to facilitate the extraction of both electronics and holes from the active layer for the first time. The performance of these devices were compared to the performance of devices grown at the same condition, but without the AlSb barrier layers. The processed devices with the AlSb barrier show a peak responsivity of about 1.2 A/W with Johnson noise limited detectivity of 1.1 X 10¹¹ cm·Hz^½/W at 8 μm at 80 K at zero bias. The details of the modeling, growth, and characterizations will be presented. [reprint (PDF)]
15.	Photoluminescence characteristics of polar and nonpolar AlGaN/GaN superlattices Z. Vashaei, C. Bayram, P. Lavenus, and M. Razeghi Applied Physics Letters, Vol. 97, No. 12, p. 121918-1-- September 20, 2010 ...[Visit Journal] High quality Al_0.2Ga_0.8N/GaN superlattices (SLs) with various (GaN) well widths (1.6 to 6.4 nm) have been grown on polar c-plane and nonpolar m-plane freestanding GaN substrates by metal-organic chemical vapor deposition. Atomic force microscopy, high resolution x-ray diffraction, and photoluminescence (PL) studies of SLs have been carried out to determine and correlate effects of well width and polarization field on the room-temperature PL characteristics. A theoretical model was applied to explain PL energy-dependency on well width and crystalline orientation taking into account internal electric field for polar substrate. Absence of induced-internal electric field in nonpolar SLs was confirmed by stable PL peak energy and stronger PL intensity as a function of excitation power density than polar ones. [reprint (PDF)]
15.	Advances in UV sensitive visible blind GaN-based APDs M. Ulmer, R. McClintock and M. Razeghi SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol. 7945, p. 79451G-- January 23, 2011 ...[Visit Journal] In this paper, we describe our current state-of-the-art process of making visible-blind APDs based on GaN. We have grown our material on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs are compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes. Single photon detection capabilities with over 30% are demonstrated. We show how with pulse height discrimination the Geiger-mode operation conditions can be optimized for enhanced SPDE versus dark counts. [reprint (PDF)]
15.	High power photonic crystal distributed feedback quantum cascade lasers emitting at 4.5 micron B. Gokden, S. Slivken and M. Razeghi SPIE Proceedings, San Francisco, CA (January 22-28, 2010), Vol. 7608, p. 760806-1-- January 22, 2010 ...[Visit Journal] Quantum cascade lasers possess very small linewidth enhancement factor, which makes them very prominent candidates for realization of high power, nearly diffraction limited and single mode photonic crystal distributed feedback broad area lasers in the mid-infrared frequencies. In this paper, we present room temperature operation of a two dimensional photonic crystal distributed feedback quantum cascade laser emitting at 4.5 µm. peak power up to ~0.9 W per facet is obtained from a 2 mm long laser with 100 µm cavity width at room temperature. The observed spectrum is single mode with a very narrow linewidth. Far-field profile has nearly diffraction limited single lobe with full width at half maximum of 3.5 degree normal to the facet. The mode selection and power output relationships are experimentally established with respect to different cavity lengths for photonic crystal distributed feedback quantum cascade lasers. [reprint (PDF)]
15.	High-Power Continuous-Wave Operation of a 6 µm Quantum-Cascade Laser at Room Temperature J.S. Yu, S. Slivken, A. Evans, L. Doris, and M. Razeghi Applied Physics Letters, 83 (13)-- September 29, 2003 ...[Visit Journal] We report continuous-wave (cw) operation of quantum-cascade lasers (λ= 6 µm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 308 K (35 °C). The high cw optical output powers of 132 mW at 293 K and 21 mW at 308 K are achieved with threshold current densities of 2.29 and 2.91 kA/cm², respectively, for a high-reflectivity-coated 15 µm wide and 2 mm long laser. [reprint (PDF)]
15.	III-Nitride photon counting avalanche photodiodes R. McClintock, J.L. Pau, K. Minder, C. Bayram and M. Razeghi SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices V, Vol. 6900, p. 69000N-1-11.-- February 1, 2008 ...[Visit Journal] In order for solar and visible blind III-Nitride based photodetectors to effectively compete with the detective performance of PMT there is a need to develop photodetectors that take advantage of low noise avalanche gain. Furthermore, in certain applications, it is desirable to obtain UV photon counting performance. In this paper, we review the characteristics of III-nitride visible-blind avalanche photodetectors (APDs), and present the state-of-the-art results on photon counting based on the Geiger mode operation of GaN APDs. The devices are fabricated on transparent AlN templates specifically for back-illumination in order to enhance hole-initiated multiplication. The spectral response and Geiger-mode photon counting performance are analyzed under low photon fluxes, with single photon detection capabilities being demonstrated in smaller devices. Other major technical issues associated with the realization of high-quality visible-blind APDs and Geiger mode APDs are also discussed in detail and solutions to the major problems are described where available. Finally, future prospects for improving upon the performance of these devices are outlined. [reprint (PDF)]
15.	Advanced InAs/GaSb Superlattice Photovoltaic Detectors for Very-Long Wavelength Infrared Applications Y. Wei, A. Gin, M. Razeghi, and G.J. Brown Applied Physics Letters 80 (18)-- May 6, 2002 ...[Visit Journal] We report on the temperature dependence of the photoresponse of very long wavelength infrared type-II InAs/GaSb superlattice based photovoltaic detectors grown by molecular-beam epitaxy. The detectors had a 50% cutoff wavelength of 18.8 μm and a peak current responsivity of 4 A·W^-1 at 80 K. A peak detectivity of 4.5×10¹⁰ cm· Hz^½·W^-1 was achieved at 80 K at a reverse bias of 110 mV. The generation–recombination lifetime was 0.4 ns at 80 K. The cutoff wavelength increased very slowly with increasing temperature with a net shift from 20 to 80 K of only 1.2 μm [reprint (PDF)]

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