Anodic oxidation of InAlAs

The anodic oxidation of InAlAs is investigated by transmission electron microscopy, Rutherford backscattering spectroscopy and medium energy ion scattering in order to elucidate the mechanism of oxide growth. For this purpose, anodizing was carried out at 5 mA cm−2 in 0.1 M sodium tungstate and 0.1 M ammonium pentaborate electrolytes at 293 K, which results in relatively efficient film growth over an initial voltage increment of about 70 V. In this period, an amorphous oxide develops with a formation ratio of 2.0 ± 0.2 nm V−1. The film consists mainly of an outer layer of In2O3 and an inner layer of units of In2O3, Al2O3 and As2O3, the former representing about 14% of the film. There is suggestion of a fine, intermediate layer containing units of In2O3 and Al2O3 only. The layering correlates with the bond energies of the cation and oxygen species in the oxide and hence their relative migration rates. Further, for films formed in tungstate electrolyte, tungsten species are incorporated into the outer 40% of the film. Bubbles of oxygen gas are present in the film, probably developed within the In2O3 layer. At higher voltages, the film undergoes breakdown, with resulting major changes in the film morphology.