ELECTRONIC PROFILE OF N-INAS ON SEMI-INSULATING GAAS

The electron density and mobility of VPE-grown 15-μm n-type indium arsenide epilayers have been determined as a function of distance from the gallium arsenide substrate. Both epilayer surfaces show significant increases in density and decreases in mobility from the bulk values (1015-10 16 cm-3 and 105 cm2/V sec at 77 °K). The interfacial, or back, surface is apparently dominated by defects to a depth of about 3 μm. The density and mobility profiles are roughly exponential; integrated values are 1.6×1013 cm-2 and 2×103 cm2/V sec. The front surface, highly dependent on applied gate bias, has a density range in accumulation from zero to 5×1012 cm-2 and mobility from 2.5×10 4 to 3×103 cm2/V sec. The parameters for both surfaces are essentially temperature independent below 80 °K. The front-surface effective mass increases with electron density from its band-edge value of 0.0215me to nearly 0.06 me.