Selective etching of GaAs grown over AlAs etch-stop layer in buffered citric acid/H2O2 solution

Selective etching of a GaAs layer over AlAs etch-stop layer using citric acid and hydrogen peroxide unbuffered and buffered with a potassium citrate has been carefully investigated. We show that resistivity of the AlAs etch stop layer to chemical attack strongly depends on the layer thickness making the standard description based on the selectivity unusable. By considering the influence of stirring and analysing the diffusion/reaction rate limitation of the etching processes, as well as the composition of the etch-stop layer, we propose a new description of the chemical processes taking place at the AlAs etch-stop layer/etching solution interface. We also propose the best way of the etch-stop layer design for precise fabrication of electronic and optoelectronic devices grown on GaAs substrates.