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.