Indium antimonide-bismuth compositions grown by molecular beam epitaxy

Abstract

Thin films of InSb-InBi solid solutions have been prepared by molecular beam epitaxy. Using in situ reflection electron diffraction, conditions for epitaxial growth of stoichiometric layers were established on (001) and (110) surfaces of both InSb and GaAs wafers. Bi is shown to modify the diffraction patterns of (001) InSb from C(8×2) and (√2×√2) 45° to (1×3). Surface residence times of Bi were found indefinitely long (≳10 min) at temperatures ?420 °C. Bi incorporation into InSb during growth by molecular beam epitaxy is strongly dependent on Bi surface concentration, and influenced by substrate temperature and surface nonstoichiometry. Secondary ion mass spectrometry depth profiling and 2.5 MeV ion dechanneling spectra showed that ∼3% Bi can be incorporated substitutionally in Sb sites, under In rich growth conditions (largest available concentration of VSb sites). Increased Bi surface accumulation and interstitial incorporation are observed under Sb-rich surface conditions and as the relative flux of Bi is increased. Excess surface Bi forms liquid alloys with excess In during growth above 280 °C which alters the incorporation. These alloys solidify on the surface of grown films on cooling. Absorption cut-off wavelengths are unaffected by interstitial Bi concentrations; however, cutoffs out to ≳9.5 μm at 77 K are observed for Bi-doped films grown under In-rich conditions.