Optimum atomic spacing for AlAs etching in GaAs epitaxial lift-off technology

With respect to GaAs epitaxial lift-off technology, we report here the opti mum atomic spacing (5-10 nm) needed to etch off the AlAs release layer that is sandwiched between two GaAs epitaxial layers. The AlAs etching rate in hydrofluoric acid based solutions was monitored as a function of release la yer thickness. We found a sudden quenching in the etching rate, approximate ly 20 times that of the peak value, at lower dimensions (similar to2.5 nm) of the AlAs epitaxial layer. Since this cannot be explained on the basis of a previous theory (inverse square root of release layer thickness), we pro pose a diffusion-limited mechanism to explain this reaction process. With t he diffusion constant being a mean-free-path-dependent parameter, a relatio n between the mean free path and the width of the channel is considered. Th is relation is in reasonable agreement with the experimental results and gi ves a good physical insight to the reaction kinetics.