Formation of mesoporous gallium arsenide for lift-off processes by electrochemical etching

Monocrystalline, mesoporous GaAs double layers with controlled porosities are formed by means of electrochemical etching on p-type GaAs substrates using highly concentrated HF-based electrolytes. Variations in the electrolyte concentration and etching current density lead to changes in the porosity, morphology, thickness and etching rate of the porous layers. The porous layer is composed of micro and mesopores with a diameter in the range of 1 nm to 38 nm and a mean value of less than 10 nm. The etching rate of the porous layer lies in a range of 1.7 nm/sec to 1725 nm/sec. Hundred nm sized <111> oriented pyramids form at the interface between porous layer and substrate if etching current densities below 7.5 mA/cm² are applied. Mesoporous layers with thicknesses of up to 7 ¿m form reproducibly. Porous layers thicker than 7 ¿m automatically lift-off from the substrate. We demonstrate the spatially homogenous formation of mesopores on GaAs wafers with 4" in diameter. The etching rates and thicknesses values achieved indicate that etching of GaAs mesopores may be applicable to the industrial production of space solar cells.