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4.  Continuous wave, room temperature operation of λ ~ 3μm quantum cascade laser
N. Bandyopadhyay, Y. Bai, S. Tsao, S. Nida, S. Slivken and M. Razeghi
SPIE Proceedings, Vol. 8631, p. 86310M-1, Photonics West, San Francisco, CA-- February 3, 2013 ...[Visit Journal]
Quantum Cascade Lasers (QCLs), operating in continuous wave (CW) at room temperature(RT) in 3-3.5 μm spectral range, which overlaps the spectral fingerprint region of many hydrocarbons, is essential in spectroscopic trace gas detection, environment monitoring, and pollution control. A 3 μm QCL, operating in CW at RT is demonstrated. This initial result makes it possible, for the most popular material system (AlInAs/GaInAs on InP) used in QCLs in mid-infrared and long-infrared, to cover the entire spectral range of mid-infrared atmospheric window (3-5 μm). In0.79Ga0.21As/In0.11Al0.89As strain balanced superlattice, which has a large conduction band offset, was grown. The strain was balanced with composite barriers (In0.11Al0.89As /In0.4Al0.6As) in the injector region, to eliminate the need of extremely high compressively strained GaInAs, whose pseudomorphic growth is very difficult. [reprint (PDF)]
 
4.  Demonstration of shortwavelength infrared photodiodes based on type-II InAs/GaSb/AlSb superlattices
A.M. Hoang, G. Chen, A. Haddadi, S. Abdollahi Pour, and M. Razeghi
Applied Physics Letters, Vol. 100, No. 21, p. 211101-1-- May 21, 2012 ...[Visit Journal]
We demonstrate the feasibility of the InAs/GaSb/AlSb type-II superlattice photodiodes operating at the short wavelength infrared regime below 3  μm. An n-i-p type-II InAs/GaSb/AlSb photodiode was grown with a designed cut-off wavelength of 2 μm on a GaSb substrate. At 150  K, the photodiode exhibited a dark current density of 5.6 × 10−8 A/cm² and a front-side-illuminated quantum efficiency of 40.3%, providing an associated shot noise detectivity of 1.0 × 1013 Jones. The uncooled photodiode showed a dark current density of 2.2 × 10−3 A/cm² and a quantum efficiency of 41.5%, resulting in a detectivity of 1.7 × 1010 Jones [reprint (PDF)]
 
4.  Recent advances of terahertz quantum cascade lasers
Manijeh Razeghi
Proc. SPIE 8119, Terahertz Emitters, Receivers, and Applications II, 81190D (September 07, 2011)-- November 7, 2011 ...[Visit Journal]
In the past decade, tremendous development has been made in GaAs/AlGaAs based THz quantum cascade laser (QCLs), however, the maximum operating temperature is still limited below 200 K (without magnetic field). THz QCL based on difference frequency generation (DFG) represents a viable technology for room temperature operation. Recently, we have demonstrated room temperature THz emission (∼ 4 THz) up to 8.5 μW with a power conversion efficiency of 10 μW/W². A dual-period distributed feedback grating is used to filter the mid-infrared spectra in favor of an extremely narrow THz linewidth of 6.6 GHz. [reprint (PDF)]
 
4.  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)]
 
4.  Gain-length scaling in quantum dot/quantum well infrared photodetectors
T. Yamanaka, B. Movaghar, S. Tsao, S. Kuboya, A. Myzaferi and M. Razeghi
Virtual Journal of Nanoscale Science & Technology-- September 14, 2009 ...[Visit Journal][reprint (PDF)]
 
4.  Pulsed metal-organic chemical vapor deposition of high quality AlN/GaN superlattices for near-infrared intersubband transitions
C. Bayram, N. Pere-Laperne, R. McClintock, B. Fain and M. Razeghi
Applied Physics Letters, Vol. 94, No. 12, p. 121902-1-- March 23, 2009 ...[Visit Journal]
A pulsed metal-organic chemical vapor deposition technique is developed for the growth of high-quality AlN/GaN superlattices (SLs) with intersubband (ISB) transitions at optical communications wavelengths. Tunability of the AlN and GaN layers is demonstrated. Indium is shown to improve SL surface and structural quality. Capping thickness is shown to be crucial for ISB transition characteristics. Effects of barrier- and well-doping on the ISB absorption are reported. [reprint (PDF)]
 
4.  High-power mid- and far- wavelength infrared lasers for free space communication
M. Razeghi; A. Evans; J. Nguyen; Y. Bai; S. Slivken; S.R. Darvish; K. Mi
Proc. SPIE 6593, Photonic Materials, Devices, and Applications II, 65931V (June 12, 2007)-- June 12, 2007 ...[Visit Journal]
Laser-based free-space communications have been developed to serve specific roles in "last mile" high-speed data networks due to their high security, low cost, portability, and high bandwidth. Conventional free-space systems based on near infrared optical devices suffer from reliability problems due to atmospheric scattering losses and scintillation effects, such as those encountered with storms, dust, and fog. Mid-infrared wavelengths are less affected by atmospheric effects and can significantly enhance link up-time and range. This paper will discuss some of the recent advances in high-power, high temperature, high reliability mid-infrared Quantum Cascade Lasers and their potential application in highly reliable free space communication links. [reprint (PDF)]
 
4.  Optical Coatings by ion-beam sputtering deposition for long-wave infrared quantum cascade lasers
J. Nguyen, J.S. Yu, A. Evans, S. Slivken and M. Razeghi
Applied Physics Letters, 89 (11)-- September 11, 2006 ...[Visit Journal]
The authors report on the development of high-reflection and multilayer antireflection coatings using ion-beam sputtering deposition for long-wave infrared (λ~9.4 μm) quantum cascade lasers. A metallic high-reflection coating structure using Y2O3 and Au is demonstrated to achieve a high reflectance of 96.70%, and the use of a multilayer anti-reflection coating structure using PbTe and ZnO is demonstrated to achieve a very low reflectance of 1.64%. [reprint (PDF)]
 
4.  High-Power Distributed-Feedback Quantum Cascade Lasers
W.W. Bewley, I. Vurgaftman, C.S. Kim, J.R. Meyer, J. Nguyen, A.J. Evans, J.S. Yu, S.R. Darvish, S. Slivken and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 6127, pp. 612704-- January 23, 2006 ...[Visit Journal]
Recently, a distributed-feedback quantum cascade laser operating in a single spectral mode at 4.8 µm and at temperatures up to 333 K has been reported. In the present work, we provide detailed measurements and modeling of its performance characteristics. The sidemode suppression ratio exceeds 25 dB, and the emission remains robustly single-mode at all currents and temperatures tested. Cw output powers of 99 mW at 298 K and 357 mW at 200 K are obtained at currents well below the thermal rollover point. [reprint (PDF)]
 
4.  Back-illuminated solar-blind photodetectors for imaging applications
R. McClintock, A. Yasan, K. Mayes, P. Kung, and M. Razeghi
SPIE Conference, Jose, CA, Vol. 5732, pp.175-- January 22, 2005 ...[Visit Journal]
Back-illuminated solar-blind ultraviolet p-i-n photodetectors and focal plane arrays are investigated. We initially study single-pixel devices and then discuss the hybridization to a read-out integrated circuit to form focal plane arrays for solar-blind UV imaging. [reprint (PDF)]
 
4.  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)]
 
4.  Development of Quantum Cascade Lasers for High Peak Output Power and Low Threshold Current Density
S. Slivken and M. Razeghi
Solid State Electronics 46-- January 1, 2002 ...[Visit Journal]
Design and material optimization are used to both decrease the threshold current density and increase the output power for quantum cascade lasers. Waveguides are designed to try and minimize free-carrier and surface-plasmon absorption. Excellent material characterization is also presented, showing excellent control over layer thickness, interface quality, and doping level. Experiments are done to both optimize the injector doping level and to maximize the output power from a single aperture. At 300 K, a threshold current density as low as 1.8 kA/cm² is reported, along with peak powers of approximately 2.5 W. Strain-balanced lasers are also demonstrated at λnot, vert, similar5 μm, exhibiting threshold current densities<300 A/cm² at 80 K. These values represent the state-of-the-art for mid-infrared lasers with λ>4 μm [reprint (PDF)]
 
4.  Very high quality p-type AlxGa1-xN/GaN superlattice
A. Yasan and M. Razeghi
special ISDRS issue of Solid State Electronics Journal, 47-- January 1, 2003 ...[Visit Journal]
Very high quality p-type AlxGa1−xN/GaN superlattice has been achieved through optimization of Mg flow and period of superlattice. Theoretical model was used to optimize the structure of superlattice by choosing suitable Al compositions and superlattice periods. The experiments show that for x=0.26, the resistivity is as low as 0.19 Ω cm and hole concentration is as high as 4.2×1018 cm−3, the highest values ever reported for p-type AlGaN/GaN superlattices. Hall effect measurement and admittance spectroscopy on the samples confirm the high quality of the superlattices. The activation energy calculated for p-type GaN and p-type A0.1Ga0.9N/GaN superlattice is estimated to be not, vert, similar 125 and 3 meV respectively. [reprint (PDF)]
 
4.  Characteristics of high quality p-type AlxGa1-xN/GaN superlattices
A. Yasan, R. McClintock, S.R. Darvish, Z. Lin, K. Mi, P. Kung, and M. Razeghi
Applied Physics Letters 80 (12)-- March 18, 2002 ...[Visit Journal]
Very-high-quality p-type AlxGa1–xN/GaN superlattices have been grown by low-pressure metalorganic vapor-phase epitaxy through optimization of Mg flow and the period of the superlattice. For the superlattice with x = 26%, the hole concentration reaches a high value of 4.2×1018 cm–3 with a resistivity as low as 0.19 Ω · cm by Hall measurement. Measurements confirm that superlattices with a larger period and higher Al composition have higher hole concentration and lower resistivity, as predicted by theory. [reprint (PDF)]
 
4.  Phase-matched optical second-harmonic generation in GaN and AlN slab waveguides
D.N. Hahn, G.T. Kiehne, G.K.L. Wong, J.B. Ketterson, P. Kung, A. Saxler and M. Razeghi
Journal of Applied Physics 85 (5)-- March 1, 1999 ...[Visit Journal]
Phase-matched optical second-harmonic (SH) generation was observed in GaN and AlN slab waveguides. Phase matching was achieved by waveguide modal dispersion. By tuning the output wavelength of an optical parametric amplifier, several phased-matched SH peaks were observed in the visible spectrum covering blue to red wavelengths. The peak positions are in agreement with the values calculated using the dispersive refractive indices of the film and substrate materials. [reprint (PDF)]
 
4.  Growth and characterization of InAs/GaSb photoconductors for long wavelength infrared range
H. Mohseni, E. Michel, J. Sandven, M. Razeghi, W. Mitchel, and G. Brown
Applied Physics Letters 71 (10)-- September 8, 1997 ...[Visit Journal]
In this letter we report the molecular beam epitaxial growth and characterization of InAs/GaSb superlattices grown on semi-insulating GaAs substrates for long wavelength infrared detectors. Photoconductive detectors fabricated from the superlattices showed photoresponse up to 12 µm and peak responsivity of 5.5 V/W with Johnson noise limited detectivity of 1.33 × 109 cm·Hz½/W at 10.3 µm at 78 K. [reprint (PDF)]
 
4.  InAsSbP/InAsSb/InAs Laser Diodes λ = 3.2 μm) Grown by Low-Pressure Metalorganic Chemical Vapor Deposition
J. Diaz, G. Lukas, D. Wu, S. Kim, M. Erdtmann, E. Kaas, and M. Razeghi
Applied Physics Letters 70 (1)-- January 6, 1997 ...[Visit Journal]
We report metal–organic chemical-vapor deposition-grown double heterostructure InAsSbP/InAsSb/InAs diode lasers emitting at 3.2 μm operating at temperatures up to 220 K with threshold current density of 40 A/cm² at 77 K and characteristic temperature up to 42 K. Output powers as high as 260 mW in pulse mode and 60 mW in continuous wave operation have been obtained from an uncoated 100 μm stripe-width broad-area laser at 77 K. Comparison with theory shows that there is no significant nonradiative recombination mechanism for these lasers at 77 K. [reprint (PDF)]
 
4.  Sb-based infrared materials and photodetectors for the 3-5 and 8-12 μm range
E. Michel, J.D. Kim, S. Park, J. Xu, I. Ferguson, and M. Razeghi
SPIE Photonics West '96 'Photodetectors: Materials and Devices'; Proceedings 2685-- January 27, 1996 ...[Visit Journal]
In this paper, we report on the growth of InSb on (100) Si and (111)B GaAs substrates and the growth of InAsSb alloys for longer wavelength applications. The fabrication and characterization of photodetectors based on these materials are also reported. Both photoconductive and photovoltaic devices are investigated. The photodiodes are InSb p-i-n structures and InSb/InAs1-xSbx/InSb double heterostructures grown on (100) and (111)B semi-insulating GaAs and Si substrates by low pressure metalorganic chemical vapor deposition and solid source molecular beam epitaxy. The material parameters for device structures have been optimized through theoretical calculations based on fundamental mechanisms. InSb p-i-n photodiodes with peak responsivities approximately 103 V/W were grown on Si and (111) GaAs substrates. An InAsSb photovoltaic detector with a composition of x equals 0.85 showed photoresponse up to 13 micrometers at 300 K with a peak responsivity of 9.13 X 10-2 V/W at 8 micrometers . The R0A product of InAsSb detectors has been theoretically and experimentally analyzed. [reprint (PDF)]
 
4.  Photoconductance measurements on InTlSb/InSb/GaAs grown by low-pressure metalorganic chemical vapor deposition
P.T. Staveteig, Y.H. Choi, G. Labeyrie, E. Bigan, and M. Razeghi
Applied Physics Letters 64 (4)-- January 24, 1994 ...[Visit Journal]
We report infrared photoconductors based on InTlSb/InSb grown by low‐pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The photoresponse spectrum extends up to 8 μm at 77 K. The absolute magnitude of the photoresponse is measured as a function of bias. The specific detectivity is estimated to be 3×108 Hz½·cm·W-1 at 7 μm wavelength. [reprint (PDF)]
 
4.  Aluminum-free Quantum Well Intersubband Photodetectors with p-type GaAs Wells and lattice-matched ternary and quaternary barriers
J. Hoff, E. Bigan, G.J. Brown, and M. Razeghi
Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 2397-- February 6, 1995 ...[Visit Journal]
Acceptor doped Quantum Well Intersubband Photodetectors with GaAs wells and lattice matched barriers of both ternary (In0.49Ga0.51P) and quaternary (In0.62Ga0.38As0.22P0.78) materials have been grown on semi-insulating GaAs substrates by Low Pressure Metal Organic Chemical Vapor Deposition. Mesa devices were fabricated and subjected to a series of tests to illuminate experimentally some of the detection capabilities of the lattice matched quaternary InxGa1-xAsyP1-y system with (0 ≤ x ≤ 0.52) and (0 ≤ y ≤ 1). The observed photoresponse cut-off wavelengths are in good agreement with the activation energies observed in the temperature dependence of the dark currents. Kronig-Penney calculations were used to model the intersubband transition energies. [reprint (PDF)]
 
4.  Comparison of chemical and laser lift-off for the transfer of InGaN-based p-i-n junctions from sapphire to glass substrates
D. J. Rogers ; P. Bove ; F. Hosseini Teherani ; K. Pantzas ; T. Moudakir ; G. Orsal ; G. Patriarche ; S. Gautier ; A. Ougazzaden ; V. E. Sandana ; R. McClintock ; M. Razeghi
Proc. SPIE 8626, Oxide-based Materials and Devices IV, 862611 (March 18, 2013)-- March 18, 2013 ...[Visit Journal]
InGaN-based p-i-n structures were transferred from sapphire to soda-lime glass substrates using two approaches: (1) laser-lift-off (LLO) and thermo-metallic bonding and (2) chemical lift-off (LLO) by means sacrificial ZnO templates and direct wafer bonding. Both processes were found to function at RT and allow reclaim of the expensive single crystal substrate. Both approaches have also already been demonstrated to work for the wafer-scale transfer of III/V semiconductors. Compared with the industry-standard LLO, the CLO offers the added advantages of a lattice match to InGaN with higher indium contents, no need for an interfacial adhesive layer (which facilitates electrical, optical and thermal coupling), no damaged/contaminated GaN surface layer, simplified sapphire reclaim (GaN residue after LLO may complicate reclaim) and cost savings linked to elimination of the expensive LLO process. [reprint (PDF)]
 
4.  Dual section quantum cascade lasers with wide electrical tuning
S. Slivken, N. Bandyopadhyay, S. Tsao, S. Nida, Y. Bai, Q.Y. Lu and M. Razeghi
SPIE Proceedings, Vol. 8631, p. 86310P-1, Photonics West, San Francisco, CA-- February 3, 2013 ...[Visit Journal]
This paper describes our development efforts at Northwestern University regarding dual-section sampled grating distributed feedback (SGDFB) QCLs. These devices are the same size, but have much wider electrical tuning, than a traditional DFB laser. In this paper, I will show how we have dramatically extended the monolithic tuning range of high power quantum cascade lasers with high side mode suppression. This includes individual laser element tuning of up to 50 cm-1 and 24 dB average side mode suppression. These lasers are capable of room temperature continuous operation with high power (>100 mW) output. Additionally, we have demonstrated a broad spectral coverage of over 350 cm-1 on a single chip, which is equivalent to 87.5% of the gain bandwidth. The eventual goal is to realize an extended array of such laser modules in order to continuously cover a similar or broader spectral range, similar to an external cavity device without any external components. [reprint (PDF)]
 
4.  AlGaN-based deep-ultraviolet 320 x 256 focal plane array
E. Cicek, Z. Vashaei, E.K. Huang, R. McClintock and M. Razeghi
OSA Optics Letters, Vol. 37, No. 5, p. 896-898-- March 1, 2012 ...[Visit Journal]
We report the synthesis, fabrication, and testing of a 320 × 256 focal plane array (FPA) of back-illuminated, solarblind, p-i-n, AlxGa1−xN–based detectors, fully realized within our research laboratory. We implemented a pulse atomic layer deposition technique for the metalorganic chemical vapor deposition growth of thick, high-quality, crack-free, high Al composition AlxGa1−xN layers. The FPA is hybridized to a matching ISC 9809 readout integrated circuit and operated in a SE-IR camera system. Solar-blind operation is observed throughout the array with peak detection occurring at wavelengths of 256 nm and lower, and falling off three orders of magnitude by ∼285 nm. By developing an opaque masking technology, the visible response of the ROIC is significantly reduced; thus the need for external filtering to achieve solar- and visible-blind operation is eliminated. This allows the FPA to achieve high external quantum efficiency (EQE); at 254 nm, average pixels showed unbiased peak responsivity of 75 mA∕W, which corresponds to an EQE of ∼37%. Finally, the uniformity of the FPA and imaging properties are investigated. [reprint (PDF)]
 
4.  Injector doping level dependent continuous-wave operation of InP-based QCLs at λ~ 7.3 µm above room temperature
J.S. Yu, S. Slivken, and M. Razeghi
Semiconductor Science and Technology (SST), Vol. 25, No. 12, p. 125015-- December 1, 2010 ...[Visit Journal]
We report the continuous-wave (CW) operation of InGaAs/InAlAs quantum cascade lasers (QCLs) operating at λ ~ 7.3 µm above room temperature. The injector doping level–dependent CW characteristics above room temperature are investigated for doping densities between 7 × 1016 cm−3 and 2 × 1017 cm−3. The device performance, i.e. threshold current density, output power, operating temperature and characteristic temperature, depends strongly on the injector doping density. For a relatively low injector doping density of 7 × 1016 cm−3, a high-reflectivity-coated 10 µm wide and 4 mm long laser exhibits an improved device performance with an output power of 152 mW and a threshold current density of 1.37 kA cm−2 at 298 K under CW mode, operating up to 343 K. The thermal characteristics are also analyzed by the estimation from the experimentally measured data for the QCLs with different injector doping densities. [reprint (PDF)]
 
4.  On the interface properties of ZnO/Si electroluminescent diodes
J.L. Pau, J. Piqueras, D.J. Rogers, F. Hosseini Teherani, K. Minder, R. McClintock, and M. Razeghi
Journal of Applied Physics, Vol. 107, No. 3, p. 033719-1-- February 1, 2010 ...[Visit Journal]
ZnO layers grown on n–Si(100), n+–Si(100), and n–Si(111) substrates by pulsed-laser deposition were found to give electroluminescence. Light emission was observed in the form of discrete spots for currents over 1 mA with a white appearance to the naked eye. The intensity of these spots showed an erratic behavior over time, appearing and disappearing at random, while showing an associated random telegraph noise in the current signal. Regardless the substrate used, the electroluminescence spectra had a main broadband emission centered at about 600 nm and a relatively small peak at around 380 nm which corresponds to the energy of ZnO near band edge emission. Furthermore, the devices exhibited rectifying characteristics, whose current blocking direction depended on the substrate orientation. Optimization of ZnO conductivity and performing sample growth in N2 ambient were found to be critical to enhance the emission intensity. Rutherford backscattering characterization revealed the existence of an intermixed region at the interface between ZnO and Si. To study the electronic properties at the interface, frequency dependent capacitance measurements were carried out. The junction capacitance became frequency dependent at the bias voltages at which light emission occurs due to the relatively slow trapping and generation processes at deep centers. These centers are believed to play an important role in the mechanism of light emission. [reprint (PDF)]
 

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