Inversion and accumulation layer formation at elevated temperatures in n-type GaAs-anodic oxide MIS devices

Abstract

At room temperature n-type GaAs (n-GaAs)-anodic oxide MIS devices typically exhibit some form of deep depletion mode operation which is characteristic of a low thermal generation rate for minority carriers in the semiconductor. In addition, for accumulation mode bias voltages the small signal capacitance often does not approach the oxide capacitance and instead exhibits a dispersion in which this capacitance varies with the frequency of the a.c. signal and the sweep rate of the d.c. bias voltage. In this paper, capacitance-voltage measurements taken at elevated temperatures with varying d.c. bias voltage sweep rates are reported for n-GaAs-anodic oxide MIS devices. The data indicate that a stable inversion layer is formed even at high sweep rates, and no accumulation mode capacitance dispersion is observed for a capacitance-voltage measurement frequency of up to 1 MHz at temperatures above room temperature. At high temperatures and slow sweep rates, considerable mobile ion motion in the oxide is observed. A discussion of this observation based on recently developed theories for oxide growth is presented.