Electrical characteristics of Au, Al, Cu/n-InP Schottky contacts formed on chemically cleaned and air-exposed n-InP surface

We fabricated Au, Al and Cu/n-InP (1 0 0) Schottky barrier diodes formed on chemically cleaned and air-exposed n-InP surfaces to investigate the influence of the air-grown oxide on electrical performance. The oxide layer was obtained by exposing to laboratory air for 1, 2, 4, 6 and 8 weeks before metal evaporation on a chemically cleaned InP surface. Oxide thicknesses were measured by elipsometry. The chemical composition of grown surface oxides was investigated using X-ray photoelectron spectroscopy (XPS). P2O5 and In(PO)4 were found on the air-exposed surface. Although In-oxides and In-P-oxides were found, no P-oxide was found on the chemically cleaned HF-etched surface. Both air-exposed and chemically cleaned samples have indium-rich surfaces. Furthermore, we have investigated the barrier height stabilities for 70 days. The results have shown that an increase in barrier height does not directly depend on crystal surface exposure time to air. Furthermore, Schottky metals deposited on the oxidized surface have determined an increase or decrease in barrier height with respect to reference samples. Metal–oxide, metal–crystal surface interactions are the main factors of determining Schottky barrier heights.