AIP Digital Archive
The complete reduction of oxides on the chemically polished surface of (100)InP has been obtained by exposure at 300 °C to low-pressure ammonia. The whole process was monitored by various surface techniques. In a first step, exposure to ammonia removes the weakly bonded oxygen atoms and stabilizes the one-monolayer oxide, i.e., turns the initial wet oxide to a thinner, well-defined, and more stable oxide, which should prove to be a better base for further processing. Excitation of the ammonia gas by an ion gauge, i.e., use of highly active radicals, is necessary for the second step, where the oxygen atoms strongly bonded to InP are finally completely removed. The final surface is free of all contaminants and of nitrogen, its crystal structure displays a 4×1 reconstruction, and its Fermi level is pinned at 0.8 eV above the top of the valence band, i.e., 0.2 eV lower than on the clean InP surface. It is mostly InP covered by adsorbed hydrogen, with a small coverage of indium atoms liberated by the reduction of the native oxides and grouped as metallic clusters.
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