Composition and growth of thin anodic oxides formed on InP (100)

Thin anodic oxides (<100 Å) were formed on p-InP (100) in phosphate solution (0.3 M NH4H2PO4) and in sodium tungstate solution (0.1 M Na2WO4·2H2O) at different temperatures (25 and 80°C) and potentials (1–8 V). Thickness and composition were determined by different surface-analytical techniques including Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. In general, it has been observed that double-layered films are obtained with an outer In-rich layer. The thickness of the outer layer, oxide morphology and roughness as well as the composition of the duplex structure are strongly dependent on the temperature and the composition of the electrolyte. It has been found that oxides formed in phosphate exhibit a higher stability against dissolution compared with oxides formed in tungstate. The latter contain a large amount of In2O3, which leads to poor electrical properties.