Interface state density and oxide charge measurements on the metal–anodic-oxide-InSb system

Abstract

The electrical properties of the interface between anodically grown In2O3 and n-type InSb have been studied by constructing MOS-type devices and measuring the capacitance-voltage characteristic of these at 77 K. Oxides having thicknesses between 400 and 9000 Å were prepared by anodization at constant current in 0.1N KOH. The voltage shift between the experimental and ideal theoretical curves is used to find the magnitude and sign of the surface state charge and the metal-semiconductor work-function difference. We find that the oxides consistently exhibit a positive surface state charge and on those having an Al gate electrode the work-function difference is practically zero. Bias-temperature-stress measurements on thick (tox≳2000 Å) oxides are used to evaluate the sign of the ions which are mobile at 300 K. These ions, believed to be Sb, carry a positive charge. Bias-temperature-stress measurements on thin (tox<2000 Å) oxides show effects attributed to electron injection from the InSb into traps in the oxide. At 77 K a trapped negative charge layer can change the apparent sign of the surface state charge.