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The mechanism of the UV photoenhanced wet etching of GaN is determined. The UV photoenhanced wet etching does not require an electrical contact to be made to the sample, and nitrides deposited on insulating substrates (such as sapphire) can be etched, unlike photoelectrochemical (PEC) wet etching. The present technique relies on adding an appropriate oxidizing agent, in this case, peroxydisulfate (S2O82−), to KOH solutions. In a similar mechanism to PEC wet etching, the regions of low defect density are preferentially etched, leaving regions of high electron recombination such as threading dislocations relatively intact. The threading dislocations may be physically broken off, either by stirring or by a postetch sonication of the sample in KOH solution. Smoothly etched surfaces can be obtained under the proper conditions. A noble metal mask acts in a catalytic manner, yielding etch rates approximately one order of magnitude greater than those observed using inert masks. The essential role of the free radicals, originating from the peroxydisulfate ion, in the etching reaction is confirmed. The etching reaction is more rapid for more heavily n-type doped samples, and insulating C-doped layers act as an etch stop layer.

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High-quality 800-Å-thick films of tin-doped indium oxide have been prepared by magnetron sputtering. It is shown that films with low resistivity (∼4×10−4 Ω cm) and high optical transmission (≳85% between 4000 and 8000 Å) can be prepared on low-temperature (40–180 °C) substrates with O2 partial pressures of (2–7)×10−5 Torr.

Highly conductive films of zinc oxide have been prepared by reactive rf magnetron sputtering from an oxide target. Film conductivities ranging from ∼10−8 Ω−1 cm−1 to 5×102 Ω−1 cm−1 can be obtained depending on the sputter conditions. Films with sheet resistivities of 85 Ω/⧠ showed little absorption and ∼90% transmission between λ = 4000→8000 Å. A second low power discharge at the substrate is used to initiate growth of the highly conducting material on room-temperature substrates. Thus, during the deposition of insultating ZnO, turning on this second discharge causes the deposition to ’’switch’’ from low conductivity to high conductivity material. This is of particular interest in the fabrication of semiconductor-insulator-semiconductor solar cells where precise control over the thickness of the insulating layer is necessary and where a highly transparent and conductive window-junction layer is required.