Oxidation of InAs(110) and correlated changes of electronic surface properties

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Abstract
The adsorption of unexcited, molecular oxygen at clean, cleaved InAs(110) surfaces at room temperature was monitored by AES, EELS, UPS, and a Kelvin probe under the same experimental conditions. The main oxygen uptake was found to set in at some 106 L of O2 and to proceed in two subsequent stages, T1 and T2, which are activated and immobile adsorption followed by field-aided oxide-film growth (Cabrera–Mott mechanism). The oxygen is incorporated in the top layer rather than adsorbed on it since the unchanged ionization energy indicates the absence of adsorption dipoles with moment components normal to the surface. With increasing oxygen uptake, As(3d) and In(4d) energy losses chemically shifted by 3 and 0.6 eV as well as an O(2p)-related energy loss of 6.8 eV and a O(2p)-related valence-band feature are observed to grow to the same extent as the O(510 eV) Auger line. Already at very low exposures, which result in no oxygen uptake detectable by AES, a surface band-bending builds up which saturates at some 104 L of O2. The Fermi level is then pinned at 0.13 eV above the bottom of the conduction band. Above 108 L of O2, i.e., in adsorption stage T2, the work function was found to decrease again.

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