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 V-e 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 V-e,V-i, followed by the faster nominal etch rate V-e.n. The latter part is influenced by the applied radius of curvature R via V-e.n = 3.1 + 293R(-1.2) with R in mm and V-e.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. (C) 2002 Elsevier Science B.V. All rights reserved.