Oxides of GaAs grown using various oxidation processes were analyzed with X-ray photoelectron spectroscopy (XPS). Oxides investigated were the native (naturally grown or exposed to air), the chemical (grown in boiling deionized water) and the thermal (at 350°C and 500°C in dry oxygen) ones. With the use of a spectral deconvolution technique, all types of suboxides of both As and Ga including elemental arsenic were observed in addition to well-known As2O3 and Ga2O3. Elemental arsenic is considered to be one of the oxidized forms of GaAs. As2O5 was observed in the thermal oxides. In the chemical oxide and the native oxide grown in short exposure to air, elemental arsenic is the main component of oxide, while As2O3 is the dominant species in more highly oxidized films such as the thermal oxide. XPS data suggest that oxidation of As bonded in GaAs proceeds as GaAs→elemental As (As0)→As2O (As1+)→AsO (As2+)→As2O3 (As3+)→As2O5 (As5+). Oxidation of Ga bonded in GaAs advances as GaAs→Ga2O (Ga1+)→GaO (Ga2+)→Ga2O3 (Ga3+). Angle-resolved XPS measurements and semiquantitative analyses of these data were performed and an effective thickness of each oxide was also derived with simplified assumptions. The native and the chemical oxides were nearly stoichiometric. However, the thermal oxide was substantially Ga-rich due to desorption and evaporation of As2O3 from the surface during oxidation.

Anomalous Au locations in SiO 2 /Si system of Au-contaminated and thermally oxidized n-type Si(001) have been investigated using XPS and alternating current surface photovoltage (AC SPV) techniques. On the basis of XPS analyses, in Au-contaminated (2 × 10 15 atoms/cm 2 ) and thermally oxidized Si surfaces between 823 and 973 K, the Au existed both on the top of the SiO 2 and the SiO 2 /Si interface as a cluster that did not make bonds with other elements such as O and H. The resulting Au/n-type Si Schottky barrier causes an occurrence of frequency-dependent AC SPV, demonstrating that the Si surface was depleted and/or weakly inverted. This result indicates that the Au/n-type Si Schottky barrier (calculated to be 0.70 eV) survived at the SiO 2 /Si interface even after the thermal oxidation. As the temperature increased higher than 1023 K, the Au at the SiO 2 /Si interface diffused into bulk Si, resulting in drastic reduction of AC SPV. On oxidation kinetics between 1023 and 1173 K, Au is thought to act as a catalyst and to promote the SiO 2 growth at the Si surface, resulting in enhanced oxidation.

Additions to the Spectra Lila, Lizb and LiZla.Six new spectral lines have been observed in the lithium spectrum between 200 nm and 600 nm. Possible classifications are given and discussed.

Current-voltage (I-V) characteristics of GaAs Schottky and tunnel metal–insulator–semiconductor diodes were measured at various temperatures between 100 and 400 K and analyzed on a basis of an interfacial layer model recently proposed by Maeda, Umezu, Ikoma, and Yoshimura [J. Appl. Phys. 68, 2858 (1990)]. The ideality factor n obtained from the forward I-V characteristics increased from about 1.05–1.1 to 2–3 as the temperature was decreased from 400 to 100 K. This could be interpreted as an increase in the electron occupation ratio of the interface states with decreasing temperatures. Precise measurement of the n value of the I-V curve revealed anomalous behavior as a function of the forward current, which was not observed in either amorphous or crystalline Si Schottky diodes. This seems to be related to the presence of a density peak in the interface state distribution like those proposed by Spicer, Newman, Spinat, Liliental-Weber, and Weber, [J. Vac. Sci. Technol. A 8, 2084 (1990)]. The interfacial Fermi level was demonstrated to move from the metal Fermi level as applied voltage is increased, but it hardly moved relative to the conduction band bottom. This is considered to be the first direct evidence of Fermi level pinning in I-V characteristics.

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