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Microsystem technologies have the potential to significantly improve the performance, reduce the cost, and extend the capabilities of solar power systems. These benefits are possible due to a number of significant beneficial scaling effects within solar cells, modules, and systems that are manifested as the size of solar cells decrease to the sub-millimeter range. To exploit these benefits, we are using advanced fabrication techniques to create solar cells from a variety of compound semiconductors and silicon that have lateral dimensions of 250 - 1000 µm and are 1 - 20 µm thick. These fabrication techniques come out of relatively mature microsystem technologies such as integrated circuits (IC) and microelectromechanical systems (MEMS) which provide added supply chain and scale-up benefits compared to even incumbent PV technologies.

This article summarizes the metal-organic vapor phase epitaxy (MOVPE) growth technique and its use for the growth of compound semiconductor films and devices structures. In the article, we provide a brief historical overview of MOVPE and compare it to other commonly used growth techniques. We also cover fundamental scientific aspects of MOVPE growth, including the details of the growth chemistry, kinetics, and thermodynamics of MOVPE, with particular emphasis on GaAs and GaN growth, as well as the growth of other compound semiconductor materials. Of importance for the fabrication of device structures, we will discuss in depth the role of impurities and dopants in controlling the electronic and optical properties of the grown materials. Lastly, we describe the chemical sources and equipment used for this growth technique and how recent advances in system designs have allowed for increased reactor scale-up to improve manufacturing capability.

We have investigated InAs quantum dots (QD) formed on GaAs(1 0 0) using metal-organic chemical vapor deposition. Through a combination of room temperature photoluminescence and atomic force microscopy we have characterized the quantum dots. We have determined the effect of growth rate, deposited thickness, hydride partial pressure, and temperature on QD energy levels. The window of thickness for QD formation is very small, about 3 A of InAs. By decreasing the growth rate used to deposit InAs, the ground state transition of the QD is shifted to lower energies. The formation of optically active InAs QD is very sensitive to temperature. Temperatures above 500°C do not form optically active QDs. The thickness window for QD formation increases slightly at 480°C. This is attributed to the thermal dependence of diffusion length. The AsH 3 partial pressure has a non-linear effect on the QD ground state energy.

InGaAsSb thermophotovoltaic cells and Al(Ga)AsSb cell isolation diodes have been successfully grown by MOCVD. Epitaxial growth of antimonide films is quite sensitive to small changes in growth conditions, but modern MOCVD technology has sufficient control to reproducibly generate antimonide-based devices. In this work In 0.1 Ga 0.9 As 0.09 Sb 0.91 thermophotovoltaic cells exhibit open circuit voltages of 250 mV with 60% external quantum efficiency. The electrical properties of Al(Ga)AsSb are dominated by background oxygen. Oxygenated contaminates from TESb are the major contributors to this background oxygen concentration. Both Al 0.4 Ga 0.6 As 0.04 Sb 0.96 and AlAs 0.08 Sb 0.92 cell isolation diodes have been tested. AlAs 0.08 Sb 0.92 cell isolation diodes show a reverse breakdown of 7.9 V at 0.1 A/cm 2 . An antimonide-based thermophotovoltaic monolithic interconnected module has been fabricated.

This article comprehensively reviews the growth of III–V antimony-based semiconductor materials using metal-organic chemical vapor deposition (MOCVD). It does this by first discussing the general trends found for the growth of these materials. Next the specific growth techniques are discussed for each of the antimony-based systems including the binaries InSb, GaSb, and AlSb. The growth techniques used for many of the ternaries and quaternaries of these materials are also discussed. Following this a brief description of the use of dopants, novel organometallic sources and superlattices is presented. Next, the use of common characterization techniques is presented for different types of materials. A variety of the types of devices is then presented followed by a short summary and forecast of future directions that are currently being pursued in these materials.

We describe the metal-organic chemical vapor deposition (MOCVD) growth of InAsSb/InAs and GaAsSb/GaAs(P) multiple quantum well (MQW) and InAsSb/InAsP and InAsSb/InPSb strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. We also describe the growth and initial characterization of GaAsSbN/GaAs MQW structures. By changing the layer thickness and composition of the InAsSb SLSs and MQWs, we have prepared structures with low temperature (

We report on the metal-organic chemical vapor deposition (MOCVD) of strained layer superlattices (SLSs) of InAsSb/InPSb as well as mid-infrared optically pumped lasers grown using a high-speed rotating disk reactor (RDR). The devices contain AlAsSb cladding layers and strained, type-I, InAsSb/InPSb active regions. By changing the layer thickness and composition of InAsSb/InPSb SLSs, we have prepared structures with low-temperature ( < 20 K) photoluminescence wavelengths ranging from 3.4 to 4.8 μm. We find a variation in band gap of 0.272-0.324 eV for layer thicknesses of 9.0-18.2 nm. From these data we have estimated a valence band offset for the InAsSb/InPSb interface of about 400 meV. The optical properties of the superlattices revealed an anomalous low-energy transition that can be assigned to an antimony-rich interfacial layer in the superlattice. An InAsSb/InPSb SLS, laser was grown on an InAs substrate with AlAs 0.16 Sb 0.84 cladding layers. A lasing threshold and spectrally narrowed laser emission were seen from 80-200 K, the maximum temperature where lasing occurred. The temperature dependence of the SLS laser threshold is described by a characteristic temperature, T o = 72 K, from 80 to 200 K.

We report the growth of InSb on GaAs using InAlSb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of {approximately} 0.55 {micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron nobilities of {approximately}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1{minus}x}Al{sub x}Sb buffers for compositions x{le}0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.

Gas-phase parasitic reactions among TMG, TMA, and NH3, are investigated by monitoring of the growth rate/incorporation efficiency of GaN and AlN using an in-situ optical reflectometer. It is suggested that gas phase adduct (TMA: NH{sub 3}) reactions not only reduce the incorporation efficiency of TMA but also affect the incorporation behavior of TMGa. The observed phenomena can be explained by either a synergistic gas-phase scavenging effect or a surface site-blocking effect. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN QW p-n diode structure. The UV emission at 354 nm (FWHM {approximately} 6 nm) represents the first report of LED operation from an indium-free GaN QW diode.

The authors report on recent progress and improvements in the metal-organic chemical vapor deposition (MOCVD) of mid-infrared InAsSb emitters using a high speed rotating disk reactor (RDR). The devices contain AlAsSb claddings and strained InAsSb active regions. These emitters have multi-stage, type 1, InAsSb/InAsP quantum well active regions. A semi-metal GaAsSb/InAs layer acts as an internal electron source for the multistage injection lasers and AlAsSb is the electron confinement layer. These structures are the first MOCVD multi-stage devices. Growth in an RDR was necessary to avoid the previously observed Al memory effects found in a horizontal reactor. Broadband LED`s produced 2 mW average power at 3.7 {micro}m and 80 K and 0.1 mW at 4.3 {micro}m and 300 K. a multi-stage, 3.8--3.9 {micro}m laser structure operated up to T = 180 K. At 80 K, peak-power > 100 mW/facet and a high slope efficiency (48%) were observed in these gain guided lasers.

We have grown AlxIn1−xSb epitaxial layers by metalorganic chemical vapor deposition using tritertiarybutylaluminum (TTBAl), trimethylindium (TMIn), and triethylantimony (TESb) as sources in a high speed rotating disk reactor. Growth temperatures of 435 to 505°C at 200 Torr were investigated. The V/III ratio was varied from 1.6 to 7.2 and TTBAl/(TTBAl+TMIn) ratios of 0.26 to 0.82 were investigated. AlxIn1−xSb compositions from x=0.002 to 0.52 were grown with TTBAl/(TTBAl+TMIn) ratios of 0.62 to 0.82. Under these conditions, no Al was incorporated for TTBAl/(TTBAl+TMIn) ratios less than 0.62. Hall measurements of AlxIn1−xSb showed hole concentrations between 5×1016 cm−3 to 2 × 1017 cm−3 and mobilities of 24 to 91 cm2/Vs for not intentionally doped AlxIn1−xSb.

We report in-situ optical reflectance monitoring during the metalorganic chemical vapor deposition (MOCVD) growth of (Al)GaN. In addition to the well-known thin film interference effect which enables a real-time determination of growth rate, we show that several insights about the MOCVD growth process can be gained by using this simple yet powerful technique. Illustrations from a variety of applications for in-situ reflectance monitoring, specifically the study of growth evolution, the control of alloy fractions, and the use of growth rate to gauge surface kinetics and gas injection will be reported.

Implant activation annealing of Si-implanted GaN is reported for temperatures from 1100 to 1400°C. Free electron concentrations up to 3.5×1020 cm−3 are estimated at the peak of the implanted profile with Hall mobilities of ∼60 cm2/Vs for annealing at 1300°C for 30 s with an AIN encapsulant layer. This mobility is comparable to epitaxial GaN doped at a similarly high level. For annealing at ≥1300°C, the sample must be encapsulated with AIN to prevent decomposition of the GaN layer. Channeling Rutherford backscattering demonstrates the partial removal of the implant damage after a 1400°C anneal with a minimum channeling yield of 12.6% compared to 38.6% for the as-implanted spectrum. Scanning electron microscope images show evidence of decomposition of unencapsulated GaN after a 1300°C anneal and complete sublimation after 1400°C. The use of AIN encapsulation and annealing at temperatures of ∼1300°C will allow the formation of selective areas of highly doped GaN to reduce the contact and access resistance in GaN-based transistors and thyristors.

We describe the metal-organic chemical vapor deposition (MOCVD) of InAsSb/InAs multiple quantum well (MQW) and InAsSb/InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. We have made gain-guided, injection lasers using undoped, p-type AlAs0.16Sb0.84 for optical confinement and both strained InAsSb/InAs MQW and InAsSb/InAsP SLS active regions. The lasers and light emitting diodes (LED) utilize the semi-metal properties of a p-GaAsSb/n-InAs heterojunction as a source for electrons injected into active regions. A multiple-stage LED utilizing this semi-metal injection scheme is reported. Gain-guided, injected lasers with a strained InAsSb/InAs MQW active region operated up to 210 K in pulsed mode with an emission wavelength of 3.8–3.9 μm and a characteristic temperature of 29–40 K. We also present results for both optically pumped and injection lasers with InAsSb/InAsP SLS active regions. The maximum operating temperature of an optically pumped 3.7 μm SLS laser was 240 K. An SLS LED emitted at 4.0 μm with 80 μW of power at 300 K.

We describe the metal-organic chemical vapor deposition growth of InAsSb/InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. These SLSs were grown at 500{degrees}C, and 200 torr in a horizontal quartz reactor using TMIn, TESb, AsH{sub 3},and PH{sub 3}. By changing the layer thickness and composition we have prepared structures with low temperature ({le}20K) photoluminescence wavelengths ranging from 3.2 to 4.4 {mu}m. Excellent performance was observed for an SLS LED and both optically pumped and electrically injected SLS lasers. An optically pumped, double heterostructure laser emitted at 3.86 {mu}m with a maximum operating temperature of 240 K and a characteristic temperature of 33 K. We have also made electrically injected lasers and LEDs utilizing a GaAsSb/InAs semi-metal injection scheme. The semi-metal injected, broadband LED emitted at 4 {mu}m with 80 {mu}W of power at 300K and 200 mA average current. The InAsSb/InAsP SLS injection laser emitted at 3.6 gm at 120 K.

The authors have grown AlSb and AlAs/sub x/Sb/sub 1-x/ epitaxial layers by metal-organic chemical vapour deposition (MOCVD) using trimethylamine or ethyldimethylamine alane, triethylantimony and arsine. These layers were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. The authors have examined the growth of AlAs/sub x/Sb/sub 1-x/ using temperatures of 500 to 600/spl deg/C, pressures of 65 to 630 torr, V/III ratios of 1-17, and growth rates of 0.3 to 2.7 /spl mu/m/hour in a horizontal quartz reactor. The authors have also grown gain-guided, injection lasers using AlAsSb for optical confinement and a strained InAsSb/InAs multiquantum well active region using MOCVD. The semi-metal properties of a p-GaAsSb/n-InAs heterojunction were utilised as a source for injection of electrons into the active region of the laser. In pulsed mode, the laser operated up to 210 K with an emission wavelength of 3.8-3.9 /spl mu/m. The dependence of active region composition on wavelength was determined. The authors also report on the 2-colour emission of a light-emitting diode with two different active regions to demonstrate multistage operation of these devices.

We present a comprehensive study on the growth of AlGaAs by using an alternative Al precursor, dimethylethylamine alane (DMEAA), and a Ga coprecursor, either triethylgallium (TEG) or trimethylgallium (TMG). The growth rate of AlAs determined by using in situ reflectometry was studied as a function of the growth temperature, V/III ratio, growth pressure, and rotation speed of the substrate. The presence of gas phase reactions of DMEAA with arsine and TEG was indicated, and their reduction was achieved at a lower growth pressure, lower V/III ratio, or a lower growth temperature. Negligible pre-reaction of DMEAA with TMG was observed. Excellent material uniformity of AlGaAs was achieved on a 2″ diameter wafer. Secondary ion mass spectroscopy measurements revealed extremely low C and O contents in the AlAs layer grown by DMEAA. Photoluminescence measurements suggested the presence of some non-radiative defects in the as-grown DMEAA AlGaAs layers.

We have grown AlSb and ALAsxSb1-x epitaxial layers by metalorganic chemical vapor deposition (MOCVD) using trimethylamine or ethyldimethylamine alane, triethylantimony, and arsine. These layers were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. We examined the growth of AlAsxSb1-x using temperatures of 500 to 600‡C, pressures of 65 to 630 Torr, V/III ratios of 1-17, and growth rates of 0.3 to 2.7 Μm/h in a horizontal quartz reactor. We have also grown gain-guided, injection lasers using AlAsSb for optical confinement and a strained InAsSb/lnAs multi-quantum well active region using MOCVD. The semi-metal properties of a p-GaAsSb/n-InAs heterojunction are utilized as a source for injection of electrons into the active region of the laser. In pulsed mode, the laser operated up to 210K with an emission wavelength of 3.8-3.9 Μm. The dependence of active region composition on wavelength was determined. We also report on the two-color emission of a light-emitting diode with two different active regions to demonstrate multi-stage operation of these devices.

We have grown AlSb and AlAs x sb 1-x epitaxial layers by metal-organic chemical vapor deposition (MOCVD) using trimethylamine alane or ethyldimethylamine alane, triethylantimony, and arsine. These layers were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. We examined the growth of AlAS x Sb 1-x using temperatures of 500-600°C, pressures of 65-630 Torr, V/III ratios of 1-17, and growth rates of 0.3-2.7 μm/h in a horizontal quartz reactor. We have also fabricated gain-guided, injection lasers using AlAs x Sb 1-x for optical confinement and a strained InAsSb/InAs multi-quantum well active region grown using MOCVD. In pulsed mode, the laser operated up to 210 K with an emission wavelength of 3.8-3.9 μm.

We have grown high purity AlGaAs by metalorganic chemical vapor deposition using tertiarybutylarsine (TBA), trimethylgallium, and trimethylaluminum. We have achieved p-type carrier concentrations less than 4 × 10 14 cm −3 and a mobility of 1015 cm 2 /V · s at 77 K. Photoluminescence measurements at 4 K yielded bound exciton linewidths as narrow as 4.3 meV, the narrowest reported linewidths for AlGaAs grown using TBA. Secondary ion mass spectrometry measurements found C, O, Si, and S concentrations below the instrument detection limits. A two level factorial design was used to investigate the effects of temperature, V III ratio, and group III partial pressure on the mobility, carrier concentration, and growth rate. High V III ratios at temperatures between 640–700°C gave the highest quality material. Increasing the V III ratio caused a decrease in the growth rates of both GaAs and AlGaAs using either arsine or TBA. This dependence can be explained by a competitive adsorption model where excess group V species complete with group III atoms for group III surface sites.

Strained-layer superlattices (SLS's) with biaxially compressed ${\mathrm{InAs}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ were characterized using magnetophotoluminescence and compared with unstrained ${\mathrm{InAs}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ alloys. Holes in the SLS exhibited a decrease in effective mass, approaching that of the electrons. In the two-dimensional limit, a large increase in the Auger threshold energy accompanies this strain-induced change in SLS valence-band symmetry. Correspondingly, the activation energy for nonradiative recombination in the SLS's displayed a marked increase compared with that of the unstrained alloys. Strained-layer superlattices and alloy activation energies are in agreement with estimated Auger threshold energies.

InAs{sub 1-x}Sb{sub x}/InAs strained-layer superlattice (SLS) semiconductors and thick epitaxial layers of InAs{sub 1-x}Sb{sub x} were grown under a variety of conditions by metal-organic chemical vapor deposition on InAs substrates. The III/V ratio was varied from 0.026 to 1.0 over a temperature range of 475--525C, at pressures of 200 to 660 torr and growth rates of 0.75 to 3.0 {mu}m/hour. The composition of the ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. These layers were characterized by optical microscopy, SIMS, and x-ray diffraction. The optical properties of these SLS`s were determined by infrared photoluminescence and absorption measurements. The PL peak energies of the alloys` and the SLS`s are consistently lower than the previously reported values for the bandgap of InAs{sub 1-x}Sb{sub x} alloys.

Misoriented InSb substrates were used for the growth of InSb with two new organometallic Sb sources, tris(dimethylamino)antimony (TDMASb), and tertiarybutyldimethylantimony (TBDMSb). The surface morphology of InSb grown using either TDMASb or TBDMSb was very rough for growth temperatures ≤ 425°C. This surface roughness is associated with low temperature and excess Sb or high V/III ratios. Smoother surfaces were generally found when using off-axis substrates. The details of the defects observed on the surfaces were dependent on the type of misorientation and can be related to the atomic structure of the surface steps. The smoothest surfaces were obtained for growth on InSb substrates misoriented 5° towards the ;In planes. Both n-and p-type InSb were grown using TBDMSb or TDMASb and TMIn with mobilities up to 68,990 and 7773 cm2/V · s, respectively, at 77 K. The mobility for InSb using either TDMASb or TBDMSb was improved by going to lower temperatures (400°C), pressures (215 Torr) and V/III ratios (2–4). The surface morphology improved with higher temperature (475°C), and lower pressure (215 Torr), with little or no correlation to the V/III ratio. The growth of high mobility InSb with smooth surfaces at temperatures ≤ 425°C was not achieved with TDMASb or TBDMSb and TMIn under the conditions investigated in this work.

InP1-xSbx was grown by metalorganic chemical vapor deposition under a variety of conditions. The V/III vapor phase ratio was varied from 327 to 12 over a temperature range of 450–525°C, at pressures of 77 to 660 Torr and growth rates of 0.30 to 2.0 μm/h. For some samples, the V/III vapor phase ratio was optimized for InP1-xSbx lattice matched to InAs to give smooth morphologies and lattice matching with a minimized variation of composition versus changes in the TMSb/(TMSb+PH3) ratio. Examination by transmission electron microscopy indicates that the materials are not single phase, but have undergone a spinodal decomposition, which is consistent with thermodynamic calculations. When our specimen compositions are corrected for strain relaxation, the infrared photoluminescence measurements indicate a lower energy photoluminescence peak for these materials than had been previuosly reported in the literature. Infrared absorption and photoconductivity measurements indicate no sharp band edge as would be expected for a direct gap semiconductor. The observed broad spectra are consistent with alloy decomposition.

The growth of InSb was investigated using triisopropylantimony (TIPSb) or tertiarybutyldimethylantimony (TBDMSb) and trimethylindium (TMIn) or triethylindium (TEIn) over a temperature range of 350 to 475°C and pressures between 200 and 660 Torr. The growth rates of InSb using TMIn or TEIn and either TIPSb or TBDMSb at temperatures ≤ 425°C were proportional to both the TMIn or TEIn flow rate and the temperature. The surface morphology of InSb grown using either TIPSb or TBDMSb and TMIn or TEIn was very rough for growth temperatures ≤ 425°C. The InSb with the highest mobility was grown at 400°C and a V/III ratio of 3 using TIPSb and TMIn. It was n-type with a carrier concentration of 2.5 × 1015 cm−3 and a mobility of 78,160 cm2/Vs at 77 K. Both n- and p-type InSb were grown using TBDMSb with mobilities up to 67,530 and 7773 cm2/Vs respectively, at 77 K. Only p-type InSb could be grown using TEIn and TIPSb. The mobility for InSb using either TIPSb or TBDMSb and TMIn was optimized by reducing temperatures, pressures and V/III ratios. The opposite was true for surface morphology, which improved with higher temperature, pressure, and V/III ratio. The growth of high mobility InSb with smooth surfaces at T ≤ 425°C was not achieved with TIPSb or TBDMSb and TMIn or TEIn for the growth conditions examined in this investigation.

The growth of InSb using triisopropylantimony (TIPSb) or tertiarybutyldimethylantimony (TBDMSb) and TMIn was investigated over a temperature range of 350 to 475°C. The growth rates of InSb using TMIn and either TIPSb or TBDMSb at temperatures ≤425°C were proportional to both the TMIn flow rate and the temperature. The surface morphology of InSb grown using either TIPSb or TBDMSb was very rough for growth temperatures ≤425°C. The InSb with the highest mobility was grown at 400°C and a 5/3 ratio of 3 using TIPSb. It was n-type with a carrier concentration of 2.5 × 1015 cm-3 and a mobility of 78,160 cm2/V·s at 77 K. Both n- and p-type InSb were grown using TBDMSb with mobilities up to 67,530 and 7773 cm2/V·s, respectively at 77 K. The mobility for InSb using either TIPSb or TBDMSb was optimized by going to lower temperatures, pressures and 5/3 ratios. The opposite was true for surface morphology which improved with higher temperature, pressure, and 5/3 ratio. The growth of high mobility InSb with smooth surfacestat T ≤ 425°C was not achievable with TIPSb or TBDMSb and TMIn.

Reproducible growth of InAsxSb1−x/InSb strained-layer superlattice photodiodes by low pressure metalorganic chemical vapor deposition (MOCVD) has resulted from the use of Zn doped InAsxSb1−x step-graded buffer layers. These photodiodes show improved performance with response to 10 μm and detectivities of 4 × 109 cm Hz 1 2 /W at 6 μm. Dislocation formation in InAsxSb1−x buffer layers grown on InSb substrates by MOCVD is shown to be reproducibly enhanced by p-type doping at levels exceeding the intrinsic carrier concentration at 475°C using diethylzinc. Carrier concentrations up to 6 × 1018 cm-3 were obtained. The Zn doped buffer layers have proven to be reproducibly crack free for InAsxSb1−x step graded buffer layers with a final composition of x=0.12 lattice matched to a strained layer superlattice (SLS) with an average composition of x=0.09.

The use of trimethylamine alane (TMAAl) as an alternative to trimethylaluminum (TMAl) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films has been studied in detail. AlGaAs layers were grown in a horizontal reaction chamber at 20–110 mbar with linear flow velocities as high as 3 m/s and growth temperatures in the range 650 ≤Tg≤750°C. Wafer thickness uniformity is acceptable only for the highest linear flow velocities. The 12 K photoluminescence spectra of the layers exhibit intense and narrow bound-exciton emission throughout the growth temperature range investigated. The luminescence linewidths observed are the narrowest to date for MOVPE-grown AlxGa1-xAs with x≥0.25. To assess the viability of this new source for the growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser structures were grown using TMAAl extensively. Room temperature lasing at 850 nm was reproducibly obtained, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.

Ordering on the {111} planes of the group-V sublattice (CuPt type) is demonstrated in molecular-beam-epitaxy grown ${\mathrm{InAs}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ (x\ensuremath{\approxeq}0.4) alloys and strained-layer superlattices (SLS's) using transmission electron diffraction. Accompanying ordering, a significant reduction of the band gap of the alloy was observed through infrared photoluminescence and photoconductive response measurements. An ordered SLS displayed a photoresponse at longer wavelength than the ordered alloy, due to a type-II band offset of the ordered constituents of the SLS. The band-gap reduction caused by ordering in these samples indicates that ${\mathrm{InAs}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ alloys can effectively span the 8--12-\ensuremath{\mu}m atmospheric window for long-wavelength, infrared-detector applications.

We report on the metal-organic chemical vapor deposition (MOCVD) of mid- infrared InAsSb/InPSb optically pumped lasers grown using a high speed rotating disk reactor (RDR). The devices contain AlAsSb claddings and strained, type 1, InAsSb/InPSb active regions. By changing the layer thickness and composition of InAsSb/InPSb SLSs, we have prepared structures with low temperature (

Long-wavelength magnetotransmission and photoluminescence measurements were performed on InAs{sub 0.13}Sb{sub 0.87}/InSb strained-layer superlattices (SLS's). The energies and reduced effective masses of several interband optical transitions were obtained from these experiments. SLS's with different layer thicknesses produced self-consistent results. With these data, the type-II band offset and band-edge strain-shift parameters were accurately determined. Consistent with a type-II offset, an extremely small, in-plane effective-mass hole ground state was observed, thus proving that the hole quantum well is located in the biaxially compressed, InSb layer. Nonparabolicity, suggesting valence-band anticrossing, was also observed.

There is a need for semiconductor junctions with very low leakage for energy conversion from low level radioactive or radio‐luminescent sources, and low noise blue‐green photodiodes. We report the properties of two types of GaP junctions; a Schottky barrier of Pd on liquid phase epitaxy grown n‐type GaP and a p+ over n junction grown by metal‐organic chemical vapor deposition. Both types of junctions show very low leakage currents and good efficiency for power conversion from low level beta particles, x rays, and blue‐green light.

High quality InSb epitaxial layers were grown on GaAs substrates by metalorganic chemical vapor deposition using a two-temperature growth procedure. Trimethylindium and triethyl- or trimethylantimony were used for the growth of InSb on GaAs. Transmission electron microscopy revealed the existence of a large number of misfit dislocations at the substrate-epitaxial layer interface and, in some samples, misoriented grains. The quality of the layers improved with thickness as indicated by transmission electron microscopy, X-ray rocking curve widths and Hall mobilities. The mobilities were correlated with surface roughness, X-ray rocking curve width and the Sb/In ratio. Hall mobilities up to 60,900 and 27,900 cm2/V·s were obtained at 300 and 77 K, respectively, on a 2.9 μm thick InSb layer.

Diethylselenium and tetraethyltin were investigated as n-type dopants for InSb. Carrier concentrations between 6 {times} 10{sup 15} and 4 {times} 10{sup 18} cm{sup -3} with 77 K mobilities ranging from 75, 000 to 10,000 cm{sup 2}/Vs were achieved for Sn doped InSb. Triethylantimony and trimethylindium were used to grow InSb over the temperature range of 410 {minus} 470 C with a decrease in the p-type background occurring at 410 C. Diodes were prepared using tetraethyltin, trimethylindium and trimethylantimony at 470 C. The resulting current-voltage characteristics are improved over those of diodes grown previously using dimethyltellurium. SIMS measurements indicate a diffusion coefficient for Sn in InSb at 470 C that is approximately 1 {times} 10{sup -15} cm{sup 2}/s. 8 refs., 4 figs.

High concentrations of recombination‐promoting impurities in the near‐surface region of a semiconductor can produce virtually complete suppression of carrier‐driven photochemical etching processes. In‐diffusion of Zn to levels appropriate for ohmic contact formation on GaAs (mid‐1020/cm3) has been employed to reduce etching to an undetectable level in n‐GaAs with n=1.0×1017 and 1.3×1018/cm3 and to produce a greater than ten‐fold reduction in etching of semi‐insulating GaAs. Raman spectroscopy of the altered near‐surface region shows enhanced electronic scattering, which indicates the presence of a sufficient impurity concentration to suppress etching. Transmission electron microscopy shows the near‐surface region to be crystalline without significant numbers of defects following Zn diffusion. Possible applications of this process include self‐aligned etching of transistor and laser structures.

Metalorganic chemical vapor deposition (MOCVD) for epitaxially grown InSb has been explored for infrared (IR) detector applications that incorporate a metal-insulator-semiconductor (MIS) device structure. InSb epilayers were attempted on InSb substrates with the (111)A, (111)B, and (100) surface orientations using an MOCVD process at 450° C. SiO2 insulator films were formed on these epilayers using a photon-assisted CVD process. Successful MIS fabrication was most reproducible on the (100) surface, where a large-area, featureless morphology was routinely attained. MIS devices were characterized by standard analyses of capacitance-voltage (C-V) and transient-capacitance (C-t) measurements as a function of temperature between 77 and 110 K. Epilayers that had net donor concentrations of about 1 to 3 × 1015 cm−3, the lowest achieved, demonstrated improvement for IR detector applications. For example, MIS storage times in deep depletion at 77 K exceeded 150 ms, about an order of magnitude longer than those typically measured in control samples of commercially available InSb grown by the Czochralski process. Longer storage times correlated with enhanced generation lifetimes. These relative improvements are attributed to a lower density of thermally induced defects in the epilayer material.

Magnetoluminescence measurements are shown to yield new information about the nonparabolic nature of the valence band in strained-layer structures. Detailed data for InGaAs/GaAs samples are presented and interpreted in terms of a two-band model for the nonparabolicity. 11 refs., 3 figs.

Lasers and light-emitting diodes with multistage, type I InAsSb/InAsP quantum well active regions are reported. These ten stage, cascaded devices were grown by metalorganic chemical vapor deposition. The broadband light-emitting diodes produced high average powers, >2 mW (∼80 K, 3.7 μm) and >0.1 mW (∼300 K, 4.3 μm). A 3.8–3.9 μm laser structure operated up to T=180 K. At 80 K, peak power >100 mW and a slope efficiency of 48% (4.8% per stage) were observed in our gain guided lasers. The slope efficiency was strongly dependent on cavity length, and analysis of efficiency data suggests an internal differential quantum efficiency >1 and a loss coefficient ⩾100 cm−1.

The potential for implementing quantum coherence in semiconductor self-assembled quantum dots has been investigated theoretically and experimentally. Theoretical modeling suggests that coherent dynamics should be possible in self-assembled quantum dots. Our experimental efforts have optimized InGaAs and InAs self-assembled quantum dots on GaAs for demonstrating coherent phenomena. Optical investigations have indicated the appropriate geometries for observing quantum coherence and the type of experiments for observing quantum coherence have been outlined. The optical investigation targeted electromagnetically induced transparency (EIT) in order to demonstrate an all optical delay line.

In situ optical reflectance transients reveal that the morphology evolution of the initial low-temperature buffer layer strongly influences the structural and electrical quality of the high-temperature GaN films. Moreover, the morphology evolution of that buffer layer, specifically evolution of the spatial and orientational distributions of the nuclei, is strongly affected by H2. The growth conditions for which surface smoothness is maintained throughout the two-step growth do not necessarily produce the best quality final GaN films; instead, there may be an optimal roughness and incubation period en route to the best quality final films.

The properties of InAsSb/InAsP strained-layer superlattice (SLS), midwave infrared materials, and devices are reported. SLSs were grown by metal-organic chemical vapor deposition and characterized by magnetophotoluminescence and x-ray diffraction. Excellent performance was observed for an SLS light emitting diode (LED) and an optically pumped SLS laser. The semimetal injected, broadband LED emitted at 4 μm with 80 μW of power at 300 K and 200 mA average current. The laser displayed 3.86 μm emission at 240 K, the maximum operating temperature of the laser, and a characteristic temperature of 33 K.

Gain‐guided, injection lasers using AlAsSb for optical confinement and a strained InAsSb/InAs multiquantum well active region were grown by metalorganic chemical vapor deposition. The semi‐metal properties of a p‐GaAsSb/n‐InAs heterojunction are utilized as a source for injection of electrons into the active region of the laser. In pulsed mode, the laser operated up to 210 K with an emission wavelength of 3.8–3.9 μm. We also report on the two‐color emission of a light‐emitting diode with two different active regions to demonstrate multistage operation of these ‘‘unipolar ’’ devices.

A pseudomorphic, compressively strained InAs0.94Sb0.06 multiple quantum well injection laser, emitting in the 3.5–3.6 μm range is reported. The device was grown by metalorganic chemical vapor deposition, and x‐ray and optical characterization indicate that the active region has a very low dislocation density. In pulsed mode, the laser operated at 135 K and displayed a characteristic temperature of 33 K, equaling the highest value reported for molecular‐beam epitaxy grown, InAsSb/InAlAsSb active region lasers of comparable wavelength. Factors limiting the performance of these lasers are discussed.

AlSb and AlAsxSb1−x epitaxial films grown by metalorganic chemical vapor deposition were successfully doped p‐ or n‐type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500 ° C and 76 Torr using trimethylamine alane and triethylantimony. AlAs0.16Sb0.84 films lattice matched to InAs were grown at 600 ° C and 76 Torr by adding arsine. Secondary ion mass spectroscopy showed C and O levels below 2×1018 and 6×1018 cm−3, respectively, for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn‐doped AlAs0.16Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between 1×1017 to 5×1018 cm−3 for Zn‐doped material and electron concentrations in the low to mid‐ 1018 cm−3 for Sn‐doped material.

Interband magnetophotoconductive spectroscopy was used to determine the reduced masses of several optical transitions in an InAs1−xSbx/In1−xGaxAs strained‐layer superlattice and a superlattice constituent, InAs1−xSbx alloy (x≊0.1). In both the alloy and the superlattice, light and heavy hole transitions were identified. From the light‐heavy hole splitting in the superlattice, we estimate the valence band offset and find type I behavior. Effective masses and band gap energy are measured for the CuPt ordered alloy.