Barrier and porous anodic oxides on InSb

Anodizing of InSb at 5 mA cm−2 in sodium tungstate electrolyte is shown to produce barrier-type amorphous oxide at relatively low voltages, to about 40 V, and porous-type amorphous oxide at increased voltages. The barrier-type amorphous oxide, consisting of units of In2O3 and Sb2O3, distributed relatively uniformly throughout the film, develops at a formation ratio of 2.2 ± 0.2 nm V−1. The outer 15–20% of the film also contains tungsten species. The relatively high efficiency of barrier film growth reduces significantly with transition to porous oxide, which is associated additionally with generation of oxygen at the film surface. The final oxide, at 65 V, comprises pores, of typical diameter 80 nm, orientated approximately normal to the substrate and extending from a barrier region to the film surface.