A comparison of the selective etching characteristics of conventional and low-temperature-grown GaAs over AlAs by various etching solutions

In this work we report the selective etching characteristics of GaAs grown by molecular beam epitaxy oi er AlAs etch-stop layer in four etching solutions. We show that these solutions, which are commonly used for selective etching of GaAs grown at the conventional temperature of 600 degrees C (HT GaAs) are also effective for low-temperature GaAs grown at 230 degrees C with annealing at 600 degrees C (a-LT GaAs) and low-temperature-grown GaAs without annealing (LT GaAs). In these solutions, the etching rates of LT GaAs and a-LT GaAs are lower than that of HT GaAs and hence the selectivities of LT GaAs and a-LT GaAs over AlAs are lower than that of HT GaAs over AlAs. The succinic acid/H2O2 solution with pH = 4.2 was found to be the best selective etchant. Furthermore, we observed, for the first time, that the AlAs etch-stop layer tended to fail at the periphery of the etched windows, resulting in void formation if the etching was excessive. It took a longer time for this to happen in the succinic acid/H2O2 solution than in other solutions investigated.