Multiple release layer study of the intrinsic lateral etch rate of the epitaxial lift-off process

The lateral etch rate of AlGaAs in HF in the 'Epitaxial Lift-Off' (ELO) process consists of two parts, an intrinsic and a radius-induced part. The intrinsic part is studied with a new approach in which multiple release layers are introduced in one sample. By letting an essential ELO process parameter vary over the different release layers, this parameter is examined, using only samples from one wafer. In this study, the influence of thickness, aluminium fraction, and doping concentration of the release layer on the lateral etch rate is investigated. For release layers with thicknesses below 10 nm, a positive correlation between thickness and intrinsic etch rate is found. Thicker release layers do not result in higher etch rates. Increasing aluminium fractions in the AlxGa1-xAs release layers result in higher etch rates. For aluminium fractions between 0.3 and 1, this effect covers almost six orders of magnitude. From the width of the V-shaped etch slits in samples that have been etched for 12 hours or more, the selectivity, i.e., the ratio of the etch rate of AlxGa1-xAs to GaAs, is determined. Selectivities between 4.3 and 8.6x10(5) are found for x=0.3 and x=1, respectively. A variation in silicon doping is found to have no effect on the lateral etch rate, while increased zinc doping raises the etch rate significantly.