Composition and growth of anodic and thermal oxides on InP and GaAs

Research using surface analytical techniques (Auger, XPS and 16 O/ 18 O SIMS) to characterize anodic films (formed in aqueous electrolytes at ambient temperature) and thermal oxides (formed at ∼500°C) on both InP and GaAs is summarized. Anodic and thermal oxides on InP comprise an outer indium‐rich layer and an inner layer containing In 2 O 3 , phosphorus oxide and P–O compounds with indium. For anodic films, sequential 16 O/ 18 O SIMS experiments indicate oxygen ion ingress with inner layer growth at the film/substrate interface and outer layer growth of In 2 O 3 at the film/electrolyte interface. Electrical measurements performed on metal–insulator–semiconductor (MIS) structures indicate the oxides on InP to be ‘leaky’. Thermal oxides formed on GaAs in oxygen consist primarily of Ga 2 O 3 with a small amount of arsenic (a few per cent) at the outer oxide surface as both As 2 O 3 and As 2 O 5 and a significant accumulation of elemental arsenic at the oxide/substrate interface. This probably leads to a high density of electronic traps and poor electrical properties. Anodic oxides (∼40 nm thick) formed in phosphate solution, however, have better electrical properties exhibiting low current densities (up to 6 V), making these films potentially useful for device applications.