Dependence of contact resistivity and Schottky diode characteristics on dry etching induced damage of GaInAs

Abstract

GaInAs was etched in a Cl2 plasma generated with an electron cyclotron resonance source. The effects of changing etch parameters on etch rate, morphology, and surface damage were analyzed. Increased microwave power, rf power, and Cl2 percentage in Ar caused the etch rate to increase monotonically. The etch rate decreased with increasing distance and reached a maximum for a pressure of 1.0 mTorr. The etch conditions were chosen to maintain smooth morphology, which requires a balance between ion energy, ion flux, concentration of reactive species, and pressure. Ohmic contacts for transmission lines and Schottky contacts for diodes were deposited directly on the etched GaInAs surface for the evaluation of etch induced damage. It was found that the transmission line measurements were more sensitive to surface damage than the diode characteristics and the specific contact resistivity (ρc) was a more sensitive measure of the damage than sheet resistivity. Defects generated by dry etching typically caused a reduction in ρc. The contact resistivity decreased with increasing rf power and source distance. More damage was introduced when only rf power was applied, as indicated by the lower ρc compared to when both microwave and rf power were applied. Addition of 10% Cl2 in Ar dramatically reduced the damage when compared to etching only with Ar. Increasing the pressure from 0.5 to 5.0 mTorr caused an increase in ρc but a degradation in surface morphology. The damage depth was estimated to be ∼6 nm at 50 W rf power and increased to ∼18 nm at 200 W rf power. Minimal surface damage was obtained when low rf power was used. For a self-induced dc bias of −68 V (25 W rf power), ρc was 8.3×10−5 Ω cm2, similar to the control sample.