The citric acid‐hydrogen peroxide‐water system has been developed for preferential etching of normalGaAs through photoresist masks. Etching rates depend strongly on the composition of the solution and on the crystal orientation of normalGaAs , with the rates in the order (111)B > (100) > (111)A. Flat‐bottomed holes were obtained for all compositions of the solutions. The solution does not erode photoresist masks, thereby providing preferential etching of normalGaAs through such masks.

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Liquid phase epitaxial growth of GaAs crystals was performed under a mixed gas flow, a Pd-diffused H2 gas and an arsenic vapor. It is found that liquid phase epitaxy under a mixed gas flow is effective in preparing high quality GaAs epitaxial layers with nearly stoichiometric composition. By using a mixed gas atomosphere, the un-doped epitaxial layers with carrier concentrations of the order of 1012cm-3 and mobilties of 170,000cm2/V sec at 77K were obtained reproducibly. The concentration of deep impurity in the epitaxial layers grown under a mixed gas atmosphere was approximately 5∼10 times less than that of the epitaxial layers grown under a H2 gas flow. Photocapacitance measurement at room temperature shows the existence of a deep level at 1.36µm in the epitaxial layers. It seems that the deep level is related to As vacancies, and/or to As vacancies associated with Cu.

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