AU AND AL SCHOTTKY-BARRIER FORMATION ON GAAS (100) SURFACES PREPARED BY THERMAL-DESORPTION OF A PROTECTIVE ARSENIC COATING

Soft x-ray photoemission spectroscopy has been used to investigate the initial stages of Schottky barrier formation on GaAs (100) surfaces prepared by the thermal desorption of an As cap. This work was motivated by a previous study [Brillson et al., J. Vac. Sci. Technol. B 6, 1263 (1988)] of identically grown and capped samples which reported "unpinned" Schottky barrier formation, with barrier heights falling over a wide range (0.75 eV) of energies. This large energy range is a striking result, as a considerable number of prior studies on both (110) and (100) surfaces have found that all metals will pin in a narrow (0.25 eV) range near midgap. Since Au and Al are the extremes of the larger 0.75 eV span of Schottky barriers, we have studied the deposition of these two metals. We found that the barrier height measurements on the low doped n-type samples used in this work and in the paper referenced above are affected by photovoltaic effects, even at room temperature. These photovoltaic effects cause shifts in the band bending, which are an artifact of the measurement. We also performed measurements on more heavily doped samples, and the photovoltaic effects were removed. In addition, we point out that Au-Ga alloying makes the case of Au potentially misleading. With the photovoltaic effects removed, and the Au-Ga alloying carefully accounted for, we found that the barriers heights for Au and Al differ by only 0.25 eV.