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1.  Use of PLD-grown moth-eye ZnO nanostructures as templates for MOVPE growth of InGaN-based photovoltaics
Dave Rogers, V. E. Sandana, F. Hosseini Teherani, S. Gautier, G. Orsal, T. Moudakir, M. Molinari, M. Troyon, M. Peres, M. J. Soares, A. J. Neves, T. Monteiro, D. McGrouther, J. N. Chapman, H. J. Drouhin, M. Razeghi, and A. Ougazzaden
Renewable Energy and the Environment, OSA Technical Digest paper PWB3, Optical Society of America, (2011)-- November 2, 2011 ...[Visit Journal]
At this time, no abstract is available. Scopus has content delivery agreements in place with each publisher and currently contains 30 million records with an abstract. An abstract may not be present due to incomplete data, as supplied by the publisher, or is still in the process of being indexed. [reprint (PDF)]
 
1.  ZnO Thin Films & Nanostructures for Emerging Optoelectronic Applications
D.J. Rogers, F. Hosseini Teherani, V.E. Sandana, and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-28, 2010), Vol. 7605, p. 76050K-1-- January 27, 2010 ...[Visit Journal]
ZnO-based thin films and nanostructures grown by PLD for various emerging optoelectronic applications. AZO thin films are currently displacing ITO for many TCO applications due to recent improvements in attainable AZO conductivity combined with processing, cost and toxicity advantages. Advances in the channel mobilities and Id on/off ratios in ZnO-based TTFTs have opened up the potential for use as a replacement for a-Si in AM-OLED and AM-LCD screens. Angular-dependent specular reflection measurements of self-forming, moth-eye-like, nanostructure arrays grown by PLD were seen to have <0.5% reflectivity over the whole visible spectrum for angles of incidence between 10 and 60 degrees. Such nanostructures may be useful for applications such as AR coatings on solar cells. Compliant ZnO layers on mismatched/amorphous substrates were shown to have potential for MOVPE regrowth of GaN. This approach could be used as a means to facilitate lift-off of GaN-based LEDs from insulating sapphire substrates and could allow the growth of InGaN-based solar cells on cheap substrates. The green gap in InGaN-based LEDs was combated by substituting low Ts PLD n-ZnO for MOCVD n-GaN in inverted hybrid heterojunctions. This approach maintained the integrity of the InGaN MQWs and gave LEDs with green emission at just over 510 nm. Hybrid n-ZnO/p-GaN heterojunctions were also seen to have the potential for UV (375 nm) EL, characteristic of ZnO NBE emission. This suggests that there was significant hole injection into the ZnO and that such LEDs could profit from the relatively high exciton binding energy of ZnO. [reprint (PDF)]
 
1.  Minority electron unipolar photodetectors based on Type-II InAs/GaSb/AlSb superlattices for very long wavelength infrared detection
B.M. Nguyen, S. Abdollahi Pour, S. Bogdanov and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-28, 2010), Vol. 7608, p. 760825-1-- January 22, 2010 ...[Visit Journal]
The bandstructure tunability of Type-II antimonide-based superlattices has been significantly enhanced since the introduction of the M-structure superlattice, resulting in significant improvements of Type-II superlattice infrared detectors. By using M-structure, we developed the pMp design, a novel infrared photodetector architecture that inherits the advantages of traditional photoconductive and photovoltaic devices. This minority electron unipolar device consists of an M-structure barrier layer blocking the transport of majority holes in a p-type semiconductor, resulting in an electrical transport due to minority carriers with low current density. Applied for the very long wavelength detection, at 77K, a 14µm cutoff detector exhibits a dark current 3.3 mA·cm−2, a photoresponsivity of 1.4 A/W at 50mV bias and the associated shot-noise detectivity of 4x1010 Jones. [reprint (PDF)]
 
1.  High differential resistance type-II InAs/GaSb superlattice photodiodes for the long-wavelength infrared
A. Hood, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E. Michel and M. Razeghi
Applied Physics Letters, 89 (9)-- August 28, 2006 ...[Visit Journal]
Type-II InAs/GaSb superlattice photodiodes with a 50% cutoff wavelength ranging from 11 to 13 μm are presented. Optimization of diffusion limited photodiodes provided superlattice structures for improved injection efficiency in direct injection hybrid focal plane array applications. [reprint (PDF)]
 
1.  Continuous-wave operation of λ ~ 4.8 µm quantum-cascade lasers at room temperature
A. Evans, J.S. Yu, S. Slivken, and M. Razeghi
Applied Physics Letters, 85 (12)-- September 20, 2004 ...[Visit Journal]
Continuous-wave (cw) operation of quantum-cascade lasers emitting at λ~4.8 µm is reported up to a temperature of 323 K. Accurate control of layer thickness and strain-balanced material composition is demonstrated using x-ray diffraction. cw output power is reported to be in excess of 370 mW per facet at 293 K, and 38 mW per facet at 323 K. Room-temperature average power measurements are demonstrated with over 600 mW per facet at 50% duty cycle with over 300 mW still observed at 100% (cw) duty cycle. [reprint (PDF)]
 
1.  GaInAsP/InP 1.35 μm Double Heterostructure Laser Grown on Silicon Substrate by Metalorganic Chemical Vapor Deposition
K. Mobarhan, C. Jelen, E. Kolev, and M. Razeghi
Journal of Applied Physics 74 (1)-- July 1, 1993 ...[Visit Journal]
A 1.35 μm GaInAsP/InP double heterostructure laser has been grown on a Si substrate using low‐pressure metalorganic chemical vapor deposition. This was done without the use of a superlattice layer or a very thick InP buffer layer, which are used to prevent the dislocations from spreading into the active layer. Pulsed operation with output power of over 200 mW per facet was achieved at room temperature for broad area lasers with 20 μm width and 170 μm cavity length. The threshold current density of a 350 μm cavity length device was 9.8 kA/cm². The characteristic temperature was 66 K. [reprint (PDF)]
 
1.  ZnO Thin Film Templates for GaN-based Devices
D.J. Rogers, F. Hosseini Teherani, A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, P. Kung, M. Razeghi and G. Garry
SPIE Conference, Jose, CA, Vol. 5732, pp. 412-- January 22, 2005 ...[Visit Journal]
GaN-based optoelectronic devices are plagued by a tendency to non-radiative transitions linked to defects in the active layers. ZnO is promising as a substrate material for GaN because it has the same wurtzite structure and a relatively small lattice mismatch (~1.8%). In this paper, we discuss use of ZnO thin films as templates for GaN based LED. [reprint (PDF)]
 
1.  Quantum Dot Infrared Photodetectors: Comparison Experiment and Theory
H. Lim, W. Zhang, S. Tsao, T. Sills, J. Szafraniec, K. Mi, B. Movaghar, and M. Razeghi
Virtual Journal of Nanoscale Science and Technology 12 (9)-- August 29, 2005 ...[Visit Journal][reprint (PDF)]
 
1.  Surface leakage reduction in narrow band gap type-II antimonide-based superlattice photodiodes
E.K. Huang, D. Hoffman, B.M. Nguyen, P.Y. Delaunay and M. Razeghi
Applied Physics Letters, Vol. 94, No. 5, p. 053506-1-- February 2, 2009 ...[Visit Journal]
Inductively coupled plasma (ICP) dry etching rendered structural and electrical enhancements on type-II antimonide-based superlattices compared to those delineated by electron cyclotron resonance (ECR) with a regenerative chemical wet etch. The surface resistivity of 4×105 Ω·cm is evidence of the surface quality achieved with ICP etching and polyimide passivation. By only modifying the etching technique in the fabrication steps, the ICP-etched devices with a 9.3 µm cutoff wavelength revealed a diffusion-limited dark current density of 4.1×10−6 A/cm2 and a maximum differential resistance at zero bias in excess of 5300 Ω·cm2 at 77 K, which are an order of magnitude better in comparison to the ECR-etched devices. [reprint (PDF)]
 
1.  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)]
 
1.  Tunability of intersubband absorption from 4.5 to 5.3 µm in a GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition
N. Péré-Laperne, C. Bayram, L. Nguyen-Thê, R. McClintock, and M. Razeghi
Applied Physics Letters, Vol. 95, No. 13, p. 131109-- September 28, 2009 ...[Visit Journal]
Intersubband (ISB) absorption at wavelengths as long as 5.3 µm is realized in GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition. By employing low aluminum content Al0.2Ga0.8N barriers and varying the well width from 2.6 to 5.1 nm, ISB absorption has been tuned from 4.5 to 5.3 µm. Theoretical ISB absorption and interband emission models are developed and compared to the experimental results. The effects of band offsets and the piezoelectric fields on these superlattices are investigated. [reprint (PDF)]
 
1.  InAsSb/InAsP strained-layer superlattice injection lasers operating at 4.0 μm grown by metal-organic chemical vapor deposition
B. Lane, Z. Wu, A. Stein, J. Diaz, and M. Razeghi
Applied Physics Letters 74 (23)-- June 7, 1999 ...[Visit Journal]
We report high power mid-infrared electrical injection operation of laser diodes based on InAsSb/InAsP strained-layer superlattices grown on InAs substrate by metal-organic chemical vapor deposition. The broad-area laser diodes with 100 μm aperture and 1800 μm cavity length demonstrate peak output powers of 546 and 94 mW in pulsed and cw operation respectively at 100 K with a threshold current density as low as 100 A/cm². [reprint (PDF)]
 
1.  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)]
 
1.  Quantum Dot Infrared Photodetectors: Comparison Experiment and Theory
H. Lim, W. Zhang, S. Tsao, T. Sills, J. Szafraniec, K. Mi, B. Movaghar, and M. Razeghi
Physical Review B, 72-- August 17, 2005 ...[Visit Journal]
We present data and calculations and examine the factors that determine the detectivities in self-assembled InAs and InGaAs based quantum dot infrared photodetectors (QDIPs). We investigate a class of devices that combine good wavelength selectivity with “high detectivity.” We study the factors that limit the temperature performance of quantum dot detectors. For this we develop a formalism to evaluate the optical absorption and the electron transport properties. We examine the performance limiting factors and compare theory with experimental data. We find that the notion of a phonon bottleneck does not apply to large-diameter lenslike quantum dots, which have many closely spaced energy levels. The observed strong decrease of responsivity with temperature is ultimately due to a rapid thermal cascade back into the ground states. High temperature performance is improved by engineering the excited state to be near the continuum. The good low temperature (77 K) performance in strongly bound QDIPs is shown to be due to the high gain and the low noise achievable in these micron size devices. [reprint (PDF)]
 
1.  The importance of band alignment in VLWIR type-II InAs/GaSb heterodiodes containing the M-structure barrier
D. Hoffman, B.M. Nguyen, E.K. Huang, P.Y. Delaunay, S. Bogdanov, P. Manukar, M. Razeghi, and V. Nathan
SPIE Proceedings, San Jose, CA Volume 7222-15-- January 26, 2009 ...[Visit Journal]
The Type-II InAs/GaSb superlattice photon detector is an attractive alternative to HgCdTe photodiodes and QWIPS. The use of p+ - pi - M - N+ heterodiode allows for greater flexibility in enhancing the device performance. The utilization of the Empirical Tight Binding method gives the band structure of the InAs/GaSb superlattice and the new M- structure (InAs/GaSb/AlSb/GaSb) superlattice allowing for the band alignment between the binary superlattice and the M- superlattice to be determined and see how it affects the optical performance. Then by modifying the doping level of the M- superlattice an optimal level can be determined to achieve high detectivity, by simultaneously improving both photo-response and reducing dark current for devices with cutoffs greater than 14.5 µm. [reprint (PDF)]
 
1.  Positive and negative luminescence in binary Type-II InAs/GaSb superlattice photodiodes
D. Hoffman and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 6127, pp. 61271H-- January 23, 2006 ...[Visit Journal]
In the present work, we show measurements of both positive and negative luminescence of binary Type-II InAs/GaSb superlattice photodiodes in the 3 to 13 μm spectral range. Through a radiometric calibration technique, we demonstrate temperature independent negative luminescence efficiencies of 45 % in the midwavelength (MWIR) sample from 220 K to 320 K without anti-reflective coating and values reaching 35 % in the long wavelength infrared (LWIR) spectrum sample. [reprint (PDF)]
 
1.  Graphene versus oxides for transparent electrode applications
Sandana, V. E.; Rogers, D. J.; Teherani, F. Hosseini; Bove, P.; Razeghi, M.
Proc. SPIE 8626, Oxide-based Materials and Devices IV, 862603 (March 18, 2013)-- March 18, 2013 ...[Visit Journal]
Due to their combination of good electrical conductivity and optical transparency, Transparent Conducting Oxides (TCOs) are the most common choice as transparent electrodes for optoelectronics applications. In particular, devices, such as LEDs, LCDs, touch screens and solar cells typically employ indium tin oxide. However, indium has some significant drawbacks, including toxicity issues (which are hampering manufacturing), an increasing rarefication (due to a combination of relative scarcity and increasing demand [1]) and resulting price increases. Moreover, there is no satisfactory option at the moment for use as a p-type transparent contact. Thus alternative materials solutions are actively being sought. This review will compare the performance and perspectives of graphene with respect to TCOs for use in transparent conductor applications. [reprint (PDF)]
 
1.  High Power 3-12 μm Infrared Lasers: Recent Improvements and Future Trends
M. Razeghi, S. Slivken, A. Tahraoui, A. Matlis, and Y.S. Park
Advanced Research Workshop on Semiconductor Nanostructures, Queenstown, New Zealand; Proceedings -- February 5, 2003 ...[Visit Journal]
In this paper, we discuss the progress of quantum cascade lasers (QCLs) grown by gas-source molecular beam epitaxy. Room temperature QCL operation has been reported for lasers emitting between 5-11 μm, with 9-11 μm lasers operating up to 425 K. Laser technology for the 3-5 μm range takes advantage of a strain-balanced active layer design. We also demonstrate record room temperature peak output powers at 9 and 11 μm (2.5 and 1 W, respectively) as well as record low 80K threshold current densities (250 A/cm²) for some laser designs. Preliminary distributed feedback (DFB) results are also presented and exhibit single mode operation for 9 μm lasers at room temperature. [reprint (PDF)]
 
1.  High Temperature Continuous Wave Operation of ~8 μm Quantum Cascade Lasers
S. Slivken, A. Matlis, C. Jelen, A. Rybaltowski, J. Diaz, and M. Razeghi
Applied Physics Letters 74 (2)-- January 11, 1999 ...[Visit Journal]
We report single-mode continuous-wave operation of a λ∼8 μm quantum cascade laser at 140 K. The threshold current density is 4.2 kA/cm² at 300 K in pulsed mode and 2.5 kA/cm² at 140 K in continuous wave for 2 mm long index-guided laser cavities of 20 μm width. Wide stripe (W ∼ 100 μm), index-guided lasers from the same wafer in pulsed operation demonstrate an average T0 of 210 K with other wafers demonstrating a T0 as high as 290 K for temperatures from 80 to 300 K. This improvement in high-temperature performance is a direct result of three factors: excellent material quality, a low-loss waveguide design, and a low-leakage index-guided laser geometry. [reprint (PDF)]
 
1.  Nanoselective area growth of defect-free thick indium-rich InGaN nanostructures on sacrificial ZnO templates
Renaud Puybaret, David J Rogers, Youssef El Gmili, Suresh Sundaram, Matthew B Jordan, Xin Li, Gilles Patriarche, Ferechteh H Teherani, Eric V Sandana, Philippe Bove, Paul L Voss, Ryan McClintock, Manijeh Razeghi, Ian Ferguson, Jean-Paul Salvestrini, and Abdallah Ougazzade
Renaud Puybaret et al 2017 Nanotechnology 28 195304-- April 29, 2017 ...[Visit Journal]
Nanoselective area growth (NSAG) by metal organic vapor phase epitaxy of high-quality InGaN nanopyramids on GaN-coated ZnO/c-sapphire is reported. Nanopyramids grown on epitaxial low-temperature GaN-on-ZnO are uniform and appear to be single crystalline, as well as free of dislocations and V-pits. They are also indium-rich (with homogeneous 22% indium incorporation) and relatively thick (100 nm). These properties make them comparable to nanostructures grown on GaN and AlN/Si templates, in terms of crystallinity, quality, morphology, chemical composition and thickness. Moreover, the ability to selectively etch away the ZnO allows for the potential lift-off and transfer of the InGaN/GaN nanopyramids onto alternative substrates, e.g. cheaper and/or flexible. This technology offers an attractive alternative to NSAG on AlN/Si as a platform for the fabrication of high quality, thick and indium-rich InGaN monocrystals suitable for cheap, flexible and tunable light-emitting diodes.
 
1.  High-performance bias-selectable dual-band mid-/long-wavelength infrared photodetectors and focal plane arrays based on InAs/GaSb Type-II superlattices
M. Razeghi; A. Haddadi; A.M. Hoang; G. Chen; S. Ramezani-Darvish; P. Bijjam
Proc. SPIE 8704, Infrared Technology and Applications XXXIX, 87040S (June 11, 2013)-- June 11, 2013 ...[Visit Journal]
We report a bias selectable dual-band mid-wave infrared (MWIR) and long-wave infrared (LWIR) co-located detector with 3 μm active region thickness per channel that is highly selective and can perform under high operating temperatures for the MWIR band. Under back-side illumination, a temperature evolution study of the MWIR detector's electro-optical performance found the 300 K background-limit with 2π field-of-view to be achieved below operating temperatures of 160 K, at which the temperature's 50% cutoff wavelength was 5.2 μm. The measured current reached the system limit of 0.1 pA at 110 K for 30 μm pixel-sized diodes. At 77 K, where the LWIR channel operated with a 50% cutoff wavelength at 11.2 μm, an LWIR selectivity of ∼17% was achieved in the MWIR wave band between 3 and 4.7 μm, making the detector highly selective. [reprint (PDF)]
 
1.  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)]
 
1.  Substrate emission quantum cascade ring lasers with room temperature continuous wave operation
Y. Bai, S. Tsao, N. Bandyopadhyay, S. Slivken, Q.Y. Lu, and M. Razeghi
SPIE Proceedings, Vol. 8268, p. 82680N-- January 22, 2012 ...[Visit Journal]
We demonstrate room temperature, continuous wave operation of quantum cascade ring lasers around 5 μm with single mode operation up to 0.51 W output power. Single mode operation persists up to 0.4 W. Light is coupled out of the ring cavity through the substrate with a second order distributed feedback grating. The substrate emission scheme allows for epilayer-down bonding, which leads to room temperature continuous wave operation. The far field analysis indicates that the device operates in a high order mode. [reprint (PDF)]
 
1.  Performance characteristics of high-purity mid-wave and long-wave infrared type-II InAs/GaSb superlattice infrared photodiodes
A. Hood, M. Razeghi, V. Nathan and M.Z. Tidrow
SPIE Conference, San Jose, CA, Vol. 6127, pp. 61270U-- January 23, 2006 ...[Visit Journal]
The authors report on recent advances in the development of mid-, long-, and very long-wavelength infrared (MWIR, LWIR, and VLWIR) Type-II InAs/GaSb superlattice infrared photodiodes. The residual carrier background of binary Type-II InAs/GaSb superlattice photodiodes of cut-off wavelengths around 5 µm has been studied in the temperature range between 10 and 200 K. A four-point, capacitance-voltage technique on mid-wavelength and long-wavelength Type-II InAs/GaSb superlattice infrared photodiodes reveal residual background concentrations around 5×1014 cm-3. Additionally, recent progress towards LWIR photodiodes for focal plane array imaging applications is presented. [reprint (PDF)]
 
1.  Gas Source Molecular Beam Epitaxy Growth and Characterization of Ga0.51In0.49P/InxGa1-xAs/GaAs Modulation-doped Field-effect Transistor Structures
C. Besikci, Y. Civan, S. Ozder, O. Sen, C. Jelen, S. Slivken, and M. Razeghi
Semiconductor Science Technology 12-- January 1, 1997 ...[Visit Journal]
Lattice-matched Ga0.51In0.49P/GaAs and strained Ga0.51In0.49P/InxGa1−xAs/GaAs (0.1 ≤ x ≤ 0.25) modulation-doped field-effect transistor structures were grown by gas source molecular beam epitaxy by using Si as dopant. Detailed electrical characterization results are presented. The Ga0.5In0.49P/In0.25Ga0.75As/GaAs sample yielded dark two-dimensional electron gas densities of 3.75 x 1012 cm-2 (300 K) and 2.3 x 1012 cm-2 (77 K) which are comparable to the highest sheet electron densities reported in AlGaAs/InGaAs/GaAs and InAlAs/InGaAs/InP modulation-doped heterostructures. Persistent photoconductivity was observed in the strained samples only. A 0.797 eV deep level has been detected in the undoped GaInP layers of the structures. Another level, with DLTS peak height dependent on the filling pulse width, has been detected at the interface of the strained samples. Based on the DLTS and Hall effect measurement results, this level, which seems to be the origin of persistent photoconductivity, can be attributed to the strain relaxation related defects. [reprint (PDF)]
 

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