Growth and structural characterization of GaInAsSb films on GaSb substrates

GaSb thermophotovoltaic (TPV) cells are believed to be a suitable choice for modern TPV generators, both in terms of efficiency and simplicity of the diffusion technology used. Two specific compositions (i.e. Ga0.9In0.1As0.1Sb0.9 and Ga0.82In0.18As0.17Sb0.83) of strained and partially relaxed films grown by metalorganic vapor-phase epitaxy (MOVPE) on (1 0 0) 2 degrees (sic) < 1 1 0 > GaSb substrates were studied by conventional and high-resolution transmission electron microscopy (CTEM, HREM) and atomic force microscopy (AFM). The growth was performed on an industrial size AIX2600-G MOVPE reactor with a 9 x 2-in susceptor configuration. The reactor pressure was 100 mbar and the growth temperature was 575 degrees C. Both films present a weak periodic contrast perpendicular to the growth direction due to phase separation into two GaAs-rich and InSb-rich regions. This is easily explained as the GaSb-based quaternary alloys have a miscibility gap in their solid state phase diagram. Additionally, in the first film, a diffused periodic contrast was observed in cross-sectional TEM images. Finally, the AFM images of both films present surface undulation. Comparatively, due to some irregularities it seems that the first film is more relaxed than the second. (c) 2004 Elsevier B.V. All rights reserved.