EFFECTS OF RADIOFREQUENCY BIAS ON GAAS-SURFACES ETCHED BY AR-ELECTRON-CYCLOTRON-RESONANCE PLASMA

The Ar-electron-cyclotron-resonance (ECR) microwave (MW) plasma has been applied on GaAs surfaces for investigating the effects of radio-frequency bias on etching reaction and radiation damage. The etch depths as a function of the etching time gave a linear profile with etch rates of 75 and 100 Å/min for 150- and 300-W MW powers under a 4-W rf bias, respectively, but for the etch rates an exponential profile is obtained as a function of the square root of the rf bias power. The electrical characteristics of Schottky barriers fabricated on the etched surface show strong rf bias dependence. Increasing the rf bias power, the donor concentration near surface and the barrier height decrease but the ideality factor and the depletion layer width increase monotonically. The changes are attributed to the radiation damage induced by the Ar ECR plasma which becomes gradually deeper in the damage layer and higher in concentration with increasing rf bias power. The rf biasing in the ECR plasma (which has the exceptional characteristic of being applicable to semi-insulating specimens) is very similar in effect to dc biasing.