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A new method for obtaining a bare porous surface is proposed. Photo-electrochemical etching for forming a porous layer generally results a skin layer on it. The in-situ observation of the etching process revealed that the skin layer can be peeled off by introducing a dark period at the end of the porous formation process. The dark condition switched over the etching mode to an electro-polishing mode, and generated gas bubbles at the region just below the skin layer. The peeling of the skin layer is the result of lift-up by the increase of pressure in the confined bubbles.

A new liquid phase epitaxial (LPE) technique of preparing alloy layers of a desired composition lattice-mismatched with a substrate has been developed. A GaAs layer was grown on a GaP substrate through step cooling from 800°C to 795°C, followed by contact with Ga-As-P solution at a constant temperature of 795°C. This treatment led to a transformation in the composition of the grown GaAs to GaAsP. Thus a GaAsP layer with the composition of 0.65 GaAs mole fraction, which was not grown directly on GaP, could be prepared on GaP substrates.