Characterization of undoped gallium antimonide grown by metalorganic chemical vapour deposition

Metalorganic chemical vapour deposition grown GaSb films on GaAs have been optimized for combined morphology, electrical and optical properties by variations in substrate temperature and V/III ratio. The transport properties of the films grown at 540 °C depend on precursor ratios with a V/III ratio of 0.72 providing hole mobilities of around 500 cm² V^-1 s^-1 and hole concentration about 3×10¹⁶ cm^-3. For higher temperatures, the mobility decreases and the carrier concentration increases. Changing the V/III ratio for 540 °C growth results in slight mobility loss in Sb-rich conditions and severe degradation in excess Ga conditions. Comparison of experimental and theoretical temperature dependencies of mobility shows good agreement, while differences between measured hole and inferred total impurity concentrations suggest the contribution of deeper compensating impurities. Films grown at lower temperatures were found to have very good optical quality and bandgaps equal to the bulk value of 0.72 eV. Above 500 °C, the band tailing starts to develop, when substantial disorder becomes apparent at 560 °C and above. This disorder is also observed in the Raman spectra of films grown at these temperatures. For the V/III ratio the highest optical quality was obtained for films grown with V/III = 2.0. The excitonic features in absorption are observed for the first time in GaSb.