Peroxide Etching of Germanium

Abstract

Etching with 3% hydrogen peroxide is useful for removing fractional micron layers of germanium. The etching rate is insensitive to concentration, but it is sensitive to pH, showing a minimum of about 0.021 µ/min at pH 4, a region recommended for controlled etching experiments; to temperature, showing a change of a factor 2 from 20° to 30°C; and to some foreign ions, e.g., about twice as great for sulfate ions present in solutions as when phosphate ions are present. The etching rate is different for different orientations; among those tested, slowest for the [111], fastest for [201] in acid solution and [100] in alkaline solution. Mechanically polished surfaces possess an enhanced etching rate. The enhancement is removed by heavy ion bombardment, but not by light ion bombardment. The etching rate of normal germanium surfaces is not affected appreciably by heavy ion bombardment, but the etch pit density is greatly increased. Photomicrographs of the etched surfaces are given.