The formation of anodic oxides on InAs at high efficiency in sodium tungstate electrolyte

The growth of amorphous anodic oxides on InAs in aqueous sodium tungstate electrolyte at 5 mA cm(-2) has been examined using transmission electron microscopy, atomic force microscopy and Rutherford backscattering spectroscopy. Films formed at similar to 100% efficiency are two-layered, with an outer layer composed of In2O3 above an inner layer composed of units of In2O3 and As2O3. The composition of the inner layer is approximately In2O3 . 1.45As(2)O(3). The outer layer, which comprises approximately 23% of the film thickness, results from faster outward migration of In3+ ions relative to that of As3+ ions. The In2O3 layer has a low ionic density compared with the inner layer material, which may be associated with cavities observed by microscopy. The outer layer is absent from films if the efficiency is less than similar to 85%. The nm V-1 ratios for growth of single-layered and double-layered films are approximately 1.9 and 1.8, respectively. Tungsten species are present in the outer regions of the film. (C) 2000 Elsevier Science S.A. All rights reserved.