This paper discusses progress in the preparation of mid-IR GaSb-based III-V materials grown by organometallic vapor phase epitaxy (OMVPE). The growth of these materials is complex, and fundamental and practical issues associated with their growth are outlined. Approaches that have been explored to further improve the properties and performance are briefly reviewed.Recent materials and device results on GaInAsSb bulk layers and GaInAsSb/AlGaAsSb heterostructures, grown lattice matched to GaSb, are presented. State-of-the-art GaInAsSb materials and thermophotovoltaic devices have been achieved. This progress establishes the high potential of OMVPE for mid-IR GaSb-based devices. 2 IntroductionGaSb-based III-V semiconductor alloys are attractive for optoelectronic devices such as midinfrared lasers, detectors, and thermophotovoltaics (TPVs); and electronic devices such as highspeed transistors and resonant-tunneling diodes [1]. Alloys of particular interest are based on the binaries GaSb, AlSb, InSb, GaAs, AlAs, and InAs. As shown in Fig. 1 GaSb-based heterostructures have been successfully grown by all of the major epitaxial techniques, including liquid phase epitaxy, molecular beam epitaxy (MBE), and organometallic vapor phase epitaxy (OMVPE). While each of these technologies must contend with numerous challenges that are specific to the method of choice, several fundamental issues related to Sbcontaining III-V alloys exist. These include the low volatility of Sb compared to P-and Asbased alloys, which necessitates stringent control of V/III ratio; the requirement to use low growth temperatures (450 to 600 °C); the existence of a large solid phase miscibility gap for many Sb-containing alloys; and the affinity of AlSb-based alloys to incorporate O and C. As a consequence, growth of Sb-based alloys differs significantly from the more conventional As-and P-based materials, which certainly has made the development of the GaSb-based materials and devices very challenging.This paper discusses both the fundamental and practical issues associated with the growth of mid-IR GaSb-based III-V alloys grown by OMVPE, and briefly reviews approaches that have been explored to further improve the properties and performance of bulk layers as well as heterostructures. Growth considerations include the importance of suitable organometallic precursors and control of V/III ratio; miscibility gaps in ternary and quaternary alloys; C and O contamination in AlSb-based alloys; in-situ monitoring; GaSb substrate quality and preparation;and heterostructure growth. Recent materials and device results are limited to GaInAsSb and 3 AlGaAsSb alloys grown lattice matched to GaSb, since two comprehensive reviews on OMVPE growth of Sb-based materials were recently published [5,6]. Growth considerations and brief review of previous work Fundamental differences between Sb-based and P-or As-based III-V alloysOne of the early premises of OMVPE growth of III-V semiconductors was the utilization of precursors based on group III organometallics a...
Back surface reflectors have the potential to improve thermophotovoltaic (TPV) device performance though the recirculation of infrared photons. The "hybrid" back-surface reflector (BSR) TPV cell approach allows one to construct BSRs for TPV devices using conventional, high efficiency, GaInAsSb-based TPV material. The design, fabrication, and measurements of hybrid BSR-TPV cells are described. The BSR was shown to provide a 4 mV improvement in open-circuit voltage under a constant shortcircuit current, which is comparable to the 5 mV improvement theoretically predicted.Larger improvements in open-circuit voltage are expected in the future with materials improvements.
Recent data on electron and hole lifetime in quaternary lattice-matched material as well as recombination velocities for the interface of that material with GaSb and AlGaAsSb will be presented in this talk. The results were obtained in collaboration with MIT Lincoln Laboratory and Lockheed Martin Corporation.
The effects of growth interruption on the quality of GaInAsSb/AlGaAsSb heterostructures grown by organometallic vapor phase epitaxy are reported. In-situ reflectance monitoring and ex-situ characterization by high-resolution x-ray diffraction, 4K photoluminescence (PL), and time-resolved PL indicate that GaInAsSb is extremely sensitive to growth interruption time as well as the ambient atmosphere during interruption. By optimizing the interruption sequence, surface recombination velocity as low as 20 cm/s was achieved for GaInAsSb/AlGaAsSb double heterostructures. IntroductionThe performance of minority carrier devices such as light-emitting diodes, photovoltaics, and heterojunction bipolar transistors is sensitive to non-radiative recombination at heterointerfaces, and numerous studies aimed at minimizing surface recombination velocity have been reported for heterostructures comprised of GaAs-and InP-based III-V alloys [1]. More recently, III-V materials based on GaSb are being developed for optoelectronic devices operating in the midinfrared wavelength range [2]. For example, GaInAsSb/GaSb and GaInAsSb/AlGaAsSb heterostructures are of particular interest since these alloys show great potential for thermophotovoltaic (TPV) devices used to generate power from a thermal source [3]. It was reported that both GaSb and AlGaAsSb window layers are effective in reducing GaInAsSb surface recombination [4,5]. Either of these layers was shown to improve the external quantum efficiency and open-circuit voltage V oc of GaInAsSb TPV cells, which were grown by organometallic vapor phase epitaxy (OMVPE). Furthermore, device performance of TPV structures with an AlGaAsSb window is anticipated to be better compared to that with a GaSb window. GaInAsSb/AlGaAsSb/GaSb TPV cells exhibit peak internal quantum efficiency and fill factor values exceeding 94% and 70%, respectively [7,8]. These values, which are approaching theoretical limits, are achieved for structures grown with either type of window layer. The highest reported value of V oc , however, is 0.33 V and was measured for devices with an AlGaAsSb window [7]. Since this value is only about 85% of the theoretical limit, further increases in V oc should be possible. In principle, if the interface between GaInAsSb and AlGaAsSb can be improved to lower surface recombination velocity, then V oc should increase, and thus improve overall TPV cell performance.The quality of heterointerfaces in Sb-containing alloys is extremely sensitive to growth sequences, and interruptions during OMVPE growth were reported to alter the interface chemistry, degrade the interface structure, and affect device performance [9][10][11][12][13]. This paper reports the effects of interruption on the quality of GaInAsSb/(Al)Ga(As)Sb doubleheterostructures (DHs) grown by OMVPE, and the achievement of extremely low surface recombination velocity in GaInAsSb/AlGaAsSb DHs. Both the interruption time and ambient atmosphere significantly impact the stability of the GaInAsSb surface. Surface recombination...
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