Characterisation of undoped gallium antimonide grown by metalorganic chemical vapour deposition

Metalorganic chemical vapour deposition grown GaSb films on GaAs have been optimised for combined morphology, electrical and optical properties by var iations in substrate temperature and V/III ratio. The transport properties of the films grown at 540 degrees C depend on precursor ratios with a V/III ratio of 0.72 providing hole mobilities of around 500 cm(2) V-1 s(-1) and hole concentration about 3 x 10(16) cm(-3). For higher temperatures, the mo bility decreases and the carrier concentration increases. Changing the V/II I ratio for 540 degrees C growth results in slight mobility loss in Sb-rich conditions and severe degradation in excess Ga conditions. Comparison of e xperimental and theoretical temperature dependencies of mobility shows good agreement, while differences between measured hole and inferred total impu rity concentrations suggest the contribution of deeper compensating impurit ies. Films grown at lower temperatures were found to have very good optical quality and bandgaps equal to the bulk value of of 0.72 eV. Above 500 degr ees C, the band tailing starts to develop, when substantial disorder become s apparent at 560 degrees C and above. This disorder is also observed in th e Raman spectra of films grown at these temperatures. For the V/III ratio t he highest optical quality was obtained for films grown with V/III = 2.0. T he excitonic features in absorption are observed for the first time in GaSb . (C) 2000 Elsevier Science Ltd. All rights reserved.