Center for Quantum Devices - Most Downloaded Journal Articles

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14.	High‐quality GaAs/Ga0.49In0.51P superlattices grown on GaAs and silicon substrates by low‐pressure metalorganic chemical vapor deposition Available M. Razeghi; Ph. Maurel; F. Omnes; M. Defour; C. Boothroyd; W. M. Stobbs; M. Kelly J. Appl. Phys. 63, 4511–4514 (1988) -- May 1, 1988 ...[Visit Journal] We report the successful growth of Ga0.49 Iuo.5 ! P-GaAs superlattices on GaAs and Si substrates by low-pressure metalorganic chemical vapor deposition. The high quality of the structure grown on GaAs and silicon substrates has been evidenced by transmission electron microscopy photographs, that show very sharp interfaces between GaAs wells and Gao.49InO.51 P barriers, with perfect control of thicknesses and compositions. Classical Hall measurements performed on the sample further demonstrated the presence of a twodimensional electron ga.<; with a mobility at T = 4 K , fL (4 K) = 50000 cm2 1V Is, and a carrier concentration n _ (4 K) = 2,9 X 1011 em -2. GaAs/Gao.49 InO. 51 P superlattices have been used, as well as buffer layer in order to grow GaAs on silicon substrates. Mirrorlike single-crystal GaAs has thus been obtained. A GaInP IGaAs heterostructure with electron HaH mobility as high as 6000 cm2 /V Is at 300 K and 80000 cm2 /V Is at 4 K has been grown, which is the highest mobility that has yet been reported for these materials, [reprint (PDF)]
14.	Sandwich method to grow high quality AlN by MOCVD Demir , H Li, Y Robin, R McClintock, S Elagoz and M Razeghi Journal of Physics D: Applied Physics 51, pp. 085104-- February 7, 2018 ...[Visit Journal] We report pulsed atomic layer epitaxy growth of a very high crystalline quality, thick (~2 µm) and crack-free AlN material on c-plane sapphire substrates via a sandwich method using metal organic chemical vapor deposition. This sandwich method involves the introduction of a relatively low temperature (1050 °C) 1500 nm thick AlN layer between two 250 nm thick AlN layers which are grown at higher temperature (1170 °C). The surface morphology and crystalline quality remarkably improve using this sandwich method. A 2 µm thick AlN layer was realized with 33 arcsec and 136 arcsec full width at half maximum values for symmetric and asymmetric reflections of ω-scan, respectively, and it has an atomic force microscopy root-mean-square surface roughness of ~0.71 nm for a 5 × 5 µm² surface area. [reprint (PDF)]
14.	Capacitance-voltage investigation of high purity InAs/GaSb superlattice photodiodes A. Hood, D. Hoffman, Y. Wei, F. Fuchs, and M. Razeghi Applied Physics Letters 88 (6)-- February 6, 2006 ...[Visit Journal] The residual carrier backgrounds of binary type-II InAs/GaSb superlattice photodiodes with cutoff wavelengths around 5 μm have been studied in the temperature range between 20 and 200 K. By applying a capacitance-voltage measurement technique, a residual background concentration below 10¹⁵ cm^–3 has been found. [reprint (PDF)]
14.	Highly temperature insensitive quantum cascade lasers Y. Bai, N. Bandyopadhyay, S. Tsao, E. Selcuk, S. Slivken and M. Razeghi Applied Physics Letters, Vol. 97, No. 25-- December 20, 2010 ...[Visit Journal] An InP based quantum cascade laser (QCL) heterostructure emitting around 5 μm is grown with gas-source molecular beam epitaxy. The QCL core design takes a shallow-well approach to maximize the characteristic temperatures, T(0) and T(1), for operations above room temperature. A T(0) value of 383 K and a T(1) value of 645 K are obtained within a temperature range of 298–373 K. In room temperature continuous wave operation, this design gives a single facet output power of 3 W and a wall plug efficiency of 16% from a device with a cavity length of 5 mm and a ridge width of 8 μm. [reprint (PDF)]
14.	Stable single mode terahertz semiconductor sources at room temperature M. Razeghi 2011 International Semiconductor Device Research Symposium, ISDRS [6135180] (2011).-- December 7, 2011 ...[Visit Journal] Terahertz (THz) range is an area of the electromagnetic spectra which has lots of applications but it suffers from the lack of simple working devices which can emit THz radiation, such as the high performance mid-infrared (mid-IR) quantum cascade lasers (QCLs) based on InP technology. The applications for the THz can be found in astronomy and space research, biology imaging, security, industrial inspection, etc. Unlike THz QCLs based on the fundamental oscillators, which are limited to cryogenic operations, semiconductor THz sources based on nonlinear effects of mid-IR QCLs do not suffer from operating temperature limitations, because mid-IR QCLs can operate well above room temperature. THz sources based on difference frequency generation (DFG) utilize nonlinear properties of asymmetric quantum structures, such as QCL structures. [reprint (PDF)]
14.	Structural and compositional characterization of MOVPE GaN thin films transferred from sapphire to glass substrates using chemical lift-off and room temperature direct wafer bonding and GaN wafer scale MOVPE growth on ZnO-buffered sapphire S. Gautier, T. Moudakir, G. Patriarche, D.J. Rogers, V.E. Sandana, F. Hosseini Teherani, P. Bove, Y. El Gmili, K. Pantzas, Suresh Sundaram, D. Troadec, P.L. Voss, M. Razeghi, A. Ougazzaden Journal of Crystal Growth, Volume 370, Pages 63-67 (2013)-- May 1, 2013 ...[Visit Journal] GaN thin films were grown on ZnO/c-Al₂O₃ with excellent uniformity over 2 in. diameter wafers using a low temperature/pressure MOVPE process with N₂ as a carrier and dimethylhydrazine as an N source. 5 mm×5 mm sections of similar GaN layers were direct-fusion-bonded onto soda lime glass substrates after chemical lift-off from the sapphire substrates. X-Ray Diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy confirmed the bonding of crack-free wurtzite GaN films onto a glass substrate with a very good quality of interface, i.e. continuous/uniform adherence and absence of voids or particle inclusions. Using this approach, (In) GaN based devices can be lifted-off expensive single crystal substrates and bonded onto supports with a better cost-performance profile. Moreover, the approach offers the possibility of reclaiming the expensive sapphire substrate so it can be utilized again for growth. [reprint (PDF)]
14.	High Power Electrically Injected Mid-Infrared Interband Lasers Grown by LP-MOCVD B. Lane and M. Razeghi Journal of Crystal Growth 221 (1-4)-- December 1, 2000[reprint (PDF)]
14.	Reliable GaN-based resonant tunneling diodes with reproducible room-temperature negative differential resistance C. Bayram, D.K. Sadana, Z. Vashaei and M. Razeghi SPIE Proceedings, Vol. 8268, p. 826827-- January 22, 2012 ...[Visit Journal] negative differential resistance (NDR). Compared to other negative resistance devices such as (Esaki) tunnel and transferred-electron devices, RTDs operate much faster and at higher temperatures. III-nitride materials, composed of AlGaInN alloys, have wide bandgap, high carrier mobility and thermal stability; making them ideal for high power high frequency RTDs. Moreover, larger conduction band discontinuity promise higher NDR than other materials (such as GaAs) and room-temperature operation. However, earlier efforts on GaN-based RTD structures have failed to achieve a reliable and reproducible NDR. Recently, we have demonstrated for the first time that minimizing dislocation density and eliminating the piezoelectric fields enable reliable and reproducible NDR in GaN-based RTDs even at room temperature. Observation of NDR under both forward and reverse bias as well as at room and low temperatures attribute the NDR behaviour to quantum tunneling. This demonstration marks an important milestone in exploring III-nitride quantum devices, and will pave the way towards fundamental quantum transport studies as well as for high frequency optoelectronic devices such as terahertz emitters based on oscillators and cascading structures. [reprint (PDF)]
14.	Quantum cascade lasers: from tool to product M. Razeghi, Q. Y. Lu, N. Bandyopadhyay, W. Zhou, D. Heydari, Y. Bai, and S. Slivken Optics Express Vol. 23, Issue 7, pp. 8462-8475-- March 25, 2015 ...[Visit Journal] The quantum cascade laser (QCL) is an important laser source in the mid-infrared and terahertz frequency range. The past twenty years have witnessed its tremendous development in power, wall plug efficiency, frequency coverage and tunability, beam quality, as well as various applications based on QCL technology. Nowadays, QCLs can deliver high continuous wave power output up to 5.1 W at room temperature, and cover a wide frequency range from 3 to 300 μm by simply varying the material components. Broadband heterogeneous QCLs with a broad spectral range from 3 to 12 μm, wavelength agile QCLs based on monolithic sampled grating design, and on-chip beam QCL combiner are being developed for the next generation tunable mid-infrared source for spectroscopy and sensing. Terahertz sources based on nonlinear generation in QCLs further extend the accessible wavelength into the terahertz range. Room temperature continuous wave operation, high terahertz power up to 1.9 mW, and wide frequency tunability form 1 to 5 THz makes this type of device suitable for many applications in terahertz spectroscopy, imaging, and communication. [reprint (PDF)]
14.	Scale-up of the Chemical Lift-off of (In)GaN-based p-i-n Junctions from Sapphire Substrates Using Sacrificial ZnO Template Layers D. J. Rogers, S. Sundaram, Y. El Gmili, F. Hosseini Teherani, P. Bove, V. Sandana, P. L. Voss, A. Ougazzaden, A. Rajan, K.A. Prior, R. McClintock, & M. Razeghi Proc. SPIE 9364, Oxide-based Materials and Devices VI, 936424 -- March 24, 2015 ...[Visit Journal] (In)GaN p-i-n structures were grown by MOVPE on both GaN- and ZnO-coated c-sapphire substrates. XRD studies of the as-grown layers revealed that a strongly c-axis oriented wurtzite crystal structure was obtained on both templates and that there was a slight compressive strain in the ZnO underlayer which increased after GaN overgrowth. The InGaN peak position gave an estimate of 13.6at% for the indium content in the active layer. SEM and AFM revealed that the top surface morphologies were similar for both substrates, with an RMS roughness (5 μm x 5 μm) of about 10 nm. Granularity appeared slightly coarser (40nm for the device grown on ZnO vs 30nm for the device grown on the GaN template) however. CL revealed a weaker GaN near band edge UV emission peak and a stronger broad defect-related visible emission band for the structure grown on the GaN template. Only a strong ZnO NBE UV emission was observed for the sample grown on the ZnO template. Quarter-wafer chemical lift-off (CLO) of the InGaN-based p-i-n structures from the sapphire substrate was achieved by temporary-bonding the GaN surface to rigid glass support with wax and then selectively dissolving the ZnO in 0.1M HCl. XRD studies revealed that the epitaxial nature and strong preferential c-axis orientation of the layers had been maintained after lift-off. This demonstration of CLO scale-up, without compromising the crystallographic integrity of the (In)GaN p-i-n structure opens up the perspective of transferring GaN based devices off of sapphire substrates industrially. [reprint (PDF)]
14.	Stability of far fields in double heterostructure and multiple quantum well InAsSb/InPAsSb/InAs midinfrared lasers H. Yi, A. Rybaltowski, J. Diaz, D. Wu, B. Lane, Y. Xiao, and M. Razeghi Applied Physics Letters 70 (24)-- June 16, 1997 ...[Visit Journal] Far fields in perpendicular direction to the junction are investigated in double heterostructure (DH) and multiple quantum well (MQW) midwave-infrared InAsSb/InPAsSb/InAs lasers (λ = 3.2–3.6 μm). Strong broadening of the far fields in the DH lasers was observed with increases in temperature and/or current. On the contrary, MQW lasers with otherwise identical structure exhibit very stable far fields as narrow as 23° for all the operating conditions investigated. Our experiment and theoretical modeling suggest that these different behaviors of far fields in DH and MQW lasers are attributed to the refractive index fluctuation in the InAsSb laser active region. [reprint (PDF)]
14.	A detailed analysis of carrier transport in InAs0.3Sb0.7 layers grown on GaAs substrates by metalorganic chemical vapor deposition C. Besikci, Y.H. Choi, G. Labeyrie, E. Bigan and M. Razeghi with J.B. Cohen, J. Carsello, and V.P. Dravid Journal of Applied Physics 76 (10)-- November 15, 1994 ...[Visit Journal] InAs_0.3Sb_0.7 layers with mirrorlike morphology have been grown on GaAs substrates by low‐pressure metalorganic chemical vapor deposition. A room‐temperature electron Hall mobility of 2×10⁴ cm²/V· s has been obtained for a 2 μm thick layer. Low‐temperature resistivity of the layers depended on TMIn flow rate and layer thickness. Hall mobility decreased monotonically with decreasing temperature below 300 K. A 77 K conductivity profile has shown an anomalous increase in the sample conductivity with decreasing thickness except in the near vicinity of the heterointerface. In order to interpret the experimental data, the effects of different scattering mechanisms on carrier mobility have been calculated, and the influences of the lattice mismatch and surface conduction on the Hall measurements have been investigated by applying a three‐layer Hall‐effect model. Experimental and theoretical results suggest that the combined effects of the dislocations generated by the large lattice mismatch and strong surface inversion may lead to deceptive Hall measurements by reflecting typical n‐type behavior for a p‐type sample, and the measured carrier concentration may considerably be affected by the surface conduction up to near room temperature. A quantitative analysis of dislocation scattering has shown significant degradation in electron mobility for dislocation densities above 10⁷ cm⁻². The effects of dislocation scattering on hole mobility have been found to be less severe. It has also been observed that there is a critical epilayer thickness (∼1 μm) below which the surface electron mobility is limited by dislocation scattering. [reprint (PDF)]
14.	Direct growth of thick AlN layers on nanopatterned Si substrates by cantilever epitaxy Ilkay Demir, Yoann Robin, Ryan McClintock, Sezai Elagoz, Konstantinos Zekentes, and Manijeh Razeghi Phys. Status Solidi A, pp. 1–6-- September 30, 2016 ...[Visit Journal] AlN layers have been grown on 200 nm period of nanopatterned Si (111) substrates by cantilever epitaxy and compared with AlN layers grown by maskless lateral epitaxial overgrowth (LEO) on micropatterned Si (111) substrates. The material quality of 5–10 µm thick AlN grown by LEO is comparable to that of much thinner layers (2 µm) grown by cantilever epitaxy on the nanopatterned substrates. Indeed, the latter exhibited root mean square (RMS) roughness of 0.65 nm and X-ray diffraction full width at half-maximum (FWHM) of 710 arcsec along the (0002) reflection and 930 arcsec along the (10̅15) reflection. The corresponding room temperature photoluminescence spectra was dominated by a sharp band edge peak. Back emission ultra violet light emitting diodes (UV LEDs) were fabricated by flip chip bonding to patterned AlN heat sinks followed by complete Si (111) substrate removal demonstrating a peak pulsed power of ∼0.7 mW at 344 nm peak emission wavelength. The demonstrated UV LEDs were fabricated on a cost effective epitaxial structure grown on the nanopatterned Si substrate with a total thickness of 3.3 µm [reprint (PDF)]
14.	Recent advances in InAs/InAs1- xSbx/AlAs1-xSbx gap-engineered Type-II superlattice-based photodetectors Manijeh Razeghi, Abbas Haddadi, Arash Dehzangi, Romain Chevallier, Thomas Yang Proc. SPIE 10177, Infrared Technology and Applications XLIII, 1017705 -- May 9, 2017 ...[Visit Journal] InAs/InAs1-xSbx/AlAs1-xSbx type-II superlattices (T2SLs) is a system of multi-interacting quantum wells. Since its introduction, this material system has drawn a lot of attention especially for infrared detection. In recent years, InAs/InAs1- xSbx/AlAs1-xSbx T2SL material system has experienced incredible improvements in material quality, device structure designs and device fabrication process which elevated the performances of T2SL-based photodetectors to a comparable level to the state-of-the-art material systems for infrared detection such as Mercury Cadmium Telluride (MCT). In this paper, we will present the current status of InAs/InAs1-xSbx/AlAs1-xSbx T2SL-based photodetectors for detection in different infrared regions, from short-wavelength (SWIR) to long-wavelength (LWIR) infrared, and the future outlook of this material system. [reprint (PDF)]
14.	High-Power CW Mid-IR Quantum Cascade Lasers J.R. Meyer, W.W. Bewley, J.R. Lindle, I. Vurgaftman, A.J. Evans, J.S. Yu, S. Slivken, and M. Razeghi SPIE Conference, Jose, CA, -- January 22, 2005 ...[Visit Journal] We report the cw operation of quantum cascade lasers that do not require cryogenic cooling and emit at λ = 4.7-6.2 µm. At 200 K, more than 1 W of output power is obtained from 12-µm-wide stripes, with a wall-plug efficiency (η_wall) near 10%. Room-temperature cw operation has also been demonstrated, with a maximum output power of 640 mW (η_wall = 4.5%) at 6 µm and 260 mW (η_wall = 2.3%) at 4.8 µm. Far-field characterization indicates that whereas the beam quality remains close to the diffraction limit in all of the tested lasers, in the devices emitting at 6.2 µm the beam tends to steer by as much as 5-10° degrees in either direction with varying temperature and pump current. [reprint (PDF)]
14.	Broad area photonic crystal distributed feedback quantum cascade lasers emitting 34 W at λ ~ 4.36 μm B. Gokden, Y. Bai, N. Bandyopadhyay, S. Slivken and M. Razeghi Applied Physics Letters, Vol. 97, No. 13, p. 131112-1-- September 27, 2010 ...[Visit Journal] We demonstrate room temperature, high power, single mode, and diffraction limited operation of a two dimensional photonic crystal distributed feedback quantum cascade laser emitting at 4.36 μm. Total peak power up to 34 W is observed from a 3 mm long laser with 400 μm cavity width at room temperature. Far-field profiles have M2 figure of merit as low as 2.5. This device represents a significant step toward realization of spatially and spectrally pure broad area high power quantum cascade lasers. [reprint (PDF)]
14.	Fabrication of Indium Bumps for Hybrid Infrared Focal Plane Array Applications J. Jiang, S. Tsao, T. O'Sullivan, M. Razeghi, and G.J. Brown Infrared Physics and Technology, 45 (2)-- March 1, 2004 ...[Visit Journal] Hybrid infrared focal plane arrays (FPAs) have found many applications. In hybrid IR FPAs, FPA and Si read out integrated circuits (ROICs) are bonded together with indium bumps by flip-chip bonding. Taller and higher uniformity indium bumps are always being pursued in FPA fabrication. In this paper, two indium bump fabrication processes based on evaporation and electroplating techniques are developed. Issues related to each fabrication technique are addressed in detail. The evaporation technique is based on a unique positive lithography process. The electroplating method achieves taller indium bumps with a high aspect ratio by a unique “multi-stack” technique. This technique could potentially benefit the fabrication of multi-color FPAs. Finally, a proposed low-cost indium bump fabrication technique, the “bump transfer”, is given as a future technology for hybrid IR FPA fabrication. [reprint (PDF)]
14.	Long-Wavelength InAsSb Photoconductors Operated at Near Room Temperatures (200-300 K) J.D. Kim, D. Wu, J. Wojkowski, J. Piotrowski, J. Xu, and M. Razeghi Applied Physics Letters., 68 (1),-- January 1, 1996 ...[Visit Journal] Long-wavelength InAs_1−xSb_x photoconductors operated without cryogenic cooling are reported. The devices are based on p-InAs_1−xSb_x/p-InSb heterostructures grown on (100) semi-insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP‐MOCVD). Photoreponse up to 14 μm has been obtained in a sample with x=0.77 at 300 K, which is in good agreement with the measured infrared absorption spectra. The corresponding effective lifetime of ≊0.14 ns at 300 K has been derived from stationary photoconductivity. The Johnson noise limited detectivity at λ=10.6 μm is estimated to be about 3.27×10⁷ cm· Hz^½/W at 300 K. [reprint (PDF)]
14.	Growth of GaInAs‐InP multiquantum wells on garnet (GGG=Gd3Ga5O12) substrate by metalorganic chemical vapor deposition M. Razeghi; P‐L. Meunier; P. Maurel M. Razeghi, P‐L. Meunier, P. Maurel; Growth of GaInAs‐InP multiquantum wells on garnet (GGG=Gd3Ga5O12) substrate by metalorganic chemical vapor deposition. J. Appl. Phys. 15 March 1986; 59 (6): 2261–2263-- March 15, 1986 ...[Visit Journal] Ga0.47In0.53As‐InP multiquantum wells grown by low‐pressure metalorganic chemical vapor deposition on garnet (GGG=Gd3Ga5O12 with a=12.383 Å) substrates are presented for the first time. The x‐ray diffraction pattern shows that the orientation of the epitaxial layer is (111) while the underlying substrate orientation is (100). The photoluminescence at 77 K is due to the GaInAs layers. [reprint (PDF)]
14.	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)]
14.	Room temperature quantum cascade lasers with 27% wall plug efficiency Y. Bai, N. Bandyopadhyay, S. Tsao, S. Slivken and M. Razeghi Applied Physics Letters, Vol. 98, No. 18, p. 181102-1-- May 3, 2011 ...[Visit Journal] Using the recently proposed shallow-well design, we demonstrate InP based quantum cascade lasers (QCLs) emitting around 4.9 μm with 27% and 21% wall plug efficiencies in room temperature (298 K) pulsed and continuous wave (CW) operations, respectively. The laser core consists of 40 QCL-stages. The highest cw efficiency is obtained from a buried-ridge device with a ridge width of 8 μm and a cavity length of 5 mm. The front and back facets are antireflection and high-reflection coated, respectively. The maximum single facet cw power at room temperature amounts to 5.1 W. [reprint (PDF)]
14.	Chemical lift-off and direct wafer bonding of GaN/InGaN P-I-N structures grown on ZnO K. Pantzas, D.J. Rogers, P. Bove, V.E. Sandana, F.H. Teherani, Y. El Gmili, M. Molinari, G. Patriarche, L. Largeau, O. Mauguin, S. Suresh, P.L. Voss, M. Razeghi, A. Ougazzaden Journal of Crystal Growth, Volume 435, Pages 105-109-- November 7, 2015 ...[Visit Journal] p-GaN/i-InGaN/n-GaN (PIN) structures were grown epitaxially on ZnO-buffered c-sapphire substrates by metal organic vapor phase epitaxy using the industry standard ammonia precursor for nitrogen. Scanning electron microscopy revealed continuous layers with a smooth interface between GaN and ZnO and no evidence of ZnO back-etching. Energy Dispersive X-ray Spectroscopy revealed a peak indium content of just under 5at% in the active layers. The PIN structure was lifted off the sapphire by selectively etching away the ZnO buffer in an acid and then direct bonded onto a glass substrate. Detailed high resolution transmission electron microscopy and grazing incidence X-ray diffraction studies revealed that the structural quality of the PIN structures was preserved during the transfer process. [reprint (PDF)]
13.	Gallium nitride on silicon for consumer & scalable photonics C. Bayram, K.T. Shiu, Y. Zhu, C.W. Cheng, D.K. Sadana, Z. Vashaei, E. Cicek, R. McClintock and M. Razeghi SPIE Proceedings, Vol. 8631, p. 863112-1, Photonics West, San Francisco, CA-- February 4, 2013 ...[Visit Journal] Gallium Nitride (GaN) is a unique material system that has been heavily exploited for photonic devices thanks to ultraviolet-to-terahertz spectral tunability. However, without a cost effective approach, GaN technology is limited to laboratory demonstrations and niche applications. In this investigation, integration of GaN on Silicon (100) substrates is attempted to enable widespread application of GaN based optoelectronics. Controlled local epitaxy of wurtzite phase GaN on on-axis Si(100) substrates is demonstrated via metal organic chemical vapor deposition (MOCVD). CMOS-compatible fabrication scheme is used to realize [SiO2-Si{111}-Si{100}] groove structures on conventional 200-mm Si(100) substrates. MOCVD growth (surface treatment, nucleation, initiation) conditions are studied to achieve controlled GaN epitaxy on such grooved Si(100) substrates. Scanning electron microscopy and transmission electron microscopy techniques are used to determine uniformity and defectivity of the GaN. Our results show that aforementioned groove structures along with optimized MOCVD growth conditions can be used to achieve controlled local epitaxy of wurtzite phase GaN on on-axis Si(100) substrates. [reprint (PDF)]
13.	Very High Average Power at Room Temperature from λ ~ 5.9 μm Quantum Cascade Lasers J.S. Yu, S. Slivken, A. Evans, J. David and M. Razeghi Virtual Journal of Nanoscale Science & Technology 26-- May 26, 2003 ...[Visit Journal][reprint (PDF)]
13.	Geiger-mode operation of ultraviolet avalanche photodiodes grown on sapphire and free-standing GaN substrates E. Cicek, Z. Vashaei, R. McClintock, C. Bayram, and M. Razeghi Applied Physics Letters, Vol. 96, No. 26, p. 261107 (2010);-- June 28, 2010 ...[Visit Journal] GaN avalanche photodiodes (APDs) were grown on both conventional sapphire and low dislocation density free-standing (FS) c-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. At a reverse-bias of 70 V, APDs grown on sapphire substrates exhibited a dark current density of 2.7×10⁻⁴ A/cm² whereas APDs grown on FS-GaN substrates had a significantly lower dark current density of 2.1×10⁻⁶ A/cm². Under linear-mode operation, APDs grown on FS-GaN achieved avalanche gain as high as 14 000. Geiger-mode operation conditions were studied for enhanced SPDE. Under front-illumination the 625 μm² area APD yielded a SPDE of 13% when grown on sapphire substrates compared to more than 24% when grown on FS-GaN. The SPDE of the same APD on sapphire substrate increased to 30% under back-illumination—the FS-GaN APDs were only tested under front illumination due to the thick absorbing GaN substrate. [reprint (PDF)]

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