Chemical and electrical properties at the annealed Ti/GaAsf 110) interface

We present the results of a photoemission study of the annealed Ti/GaAs(110) interface, using soft x-ray (SXPS), x-ray (XPS), and ultraviolet (UPS) photoelectron spectroscopies to monitor the substrate and overlayer core levels and the valence band for Ti thicknesses between 6.7 and 20 monolayers and annealing temperatures between 200 and 425 °C. The SXPS data imply the formation of a stable Ti-As region near the Ti/GaAs interface that increases in width with temperature. Concomitant to this, the binding energy of the Ga changes from its room-temperature position towards elemental Ga. The XPS data suggest the presence of elemental Ga at or near the overlayer surface. The UPS data suggest the possibility of cluster formation on the overlayer surface. In situ current-voltage (I-V) measurements were also made on thick-film systems fabricated using similar methods to those used in the photoemission studies [i.e., cleaving, depositing metal (— 1000 A), and annealing in UHV]. The movement of Ti-As reaction products into the substrate provides a framework to explain the observed increase upon annealing of the I-V barrier height for Ti/n-GaAs Schottky contacts.