Effect of Growth Interruption on the Properties of GaInAsSb/AlGaAsSb/GaSb Heterostructures and the Performance of Thermo
- PDF / 217,996 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 228 Views
B8.4.1
Effect of Growth Interruption on the Properties of GaInAsSb/AlGaAsSb/GaSb Heterostructures and the Performance of Thermophotovoltaic Devices C.A. Wang, D.A. Shiau, M.K. Connors, L.R. Danielson1, G. Nichols1, D. Donetsky2, S. Anikeev2, G. Belenky2 Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02420-9108 1 Lockheed Martin Corporation, Schenectady, NY 12301 2 State University of New York, Stony Brook, NY 11794 ABSTRACT The effect of growth interruption on the properties of GaInAsSb/(Al)Ga(As)Sb heterostructures and on the performance of GaInAsSb/AlGaAsSb/GaSb thermophotovoltaic (TPV) devices grown by organometallic vapor phase epitaxy is reported. In-situ reflectance monitoring is shown to be sensitive for observation of surface degradation during growth interruption, and this data was correlated with materials characterization by high-resolution x-ray diffraction and 4K photoluminescence (PL). Minority-carrier lifetime by time-resolved PL was used to determine interfacial recombination velocity of GaInAsSb/AlGaAsSb and GaInAsSb/GaSb double heterostructures grown with and without interruption, respectively. GaInAsSb/AlGaAsSb TPV devices grown without growth interruption have a slightly higher performance compared to those grown with interruption. INTRODUCTION GaInAsSb/(Al)Ga(As)Sb double heterostructures, lattice matched to GaSb, are being developed for thermophotovoltaic (TPV) energy conversion systems that operate with thermal sources heated to ~1000 °C [1-9]. GaInAsSb alloys with energy gap Eg in the range 0.5 to 0.55 eV have been of particular interest and high performance TPV cells with either a GaSb or Al0.25Ga0.75As0.02Sb0.98 window layer have been reported with peak internal quantum efficiency (IQE) and fill factor (FF) values exceeding 94% and 70%, respectively [7-8]. These values, which are approaching theoretical limits, are comparable for structures grown with either type of window layer. The highest reported value of open circuit voltage Voc is 0.33 V and was measured for devices with an AlGaAsSb window. However, since this value is only about 85% of the theoretical limit [4,7], further increases in Voc should be possible. The advantage of AlGaAsSb over a GaSb as a window layer is related to the band alignments between GaInAsSb and the different window layers. The valence-band offset between ~0.53-eV Ga0.84In0.16As0.14Sb0.86 and Al0.25Ga0.75As0.02Sb0.98 is almost zero. This alignment minimizes carrier trapping at this interface, and should reduce surface recombination [2,10]. The GaInAsSb/GaSb interface is a staggered type-II band alignment that leads to electron accumulation and a comparatively higher surface recombination velocity [2,10]. Thus, structures with the AlGaAsSb window are anticipated to yield better performance than those with a GaSb window. The primary technique used to grow GaInAsSb TPV structures is organometallic vapor phase epitaxy (OMVPE) [3,5-8]. Previous growth studies reported that the metastable GaInAsSb alloy, which is susceptible to phase separat
Data Loading...
