Influence of radius of curvature on the lateral etch rate of the weight induced epitaxial lift-off process

The ‘Weight Induced Epitaxial Lift-Off’ (WI-ELO) process is used to free single crystalline films from the GaAs substrates on which they have been deposited by etching a sacrificial AlAs release layer. The lateral etch rate Ve of this process is influenced by the weight induced radius of curvature R of the film. Bulk-etch experiments of AlxGa1−x As layers were conducted to compare an unhampered etching process with WI-ELO. It is found that standard WI-ELO etching demonstrates etch rates exceeding the bulk etch rate. Further experiments have shown that the WI-ELO etch rate is not constant in time, but consists of a slow initial etch rate Ve,i, followed by the faster nominal etch rate Ve,n. The latter part is influenced by the applied radius of curvature R via Ve,n=3.1+293R−1.2 with R in mm and Ve,n in mm h−1. This result implies an etch rate consisting of a constant plus a radius-induced part, resulting in both a qualitative and quantitative discrepancy with established theory. The explanations could be the different reaction kinetics and the occurrence of stress or strain in the film.