Metal–semiconductor surface and interface states on (110) GaAs

Abstract

Photoemission studies have been carried out for aluminum and gallium metal surfaces and metal–GaAs interfaces. Core chemical shifts and valence band changes have been simultaneously investigated with the wide photon energy range available on the 4° beam line at the Stanford Synchrotron Radiation Laboratory. These experiments show that although studies of the individual surfaces provide useful reference information, the separate character of the free surfaces is dominated upon interface formation by chemical changes and bond formation. The studies have shown that, for a simple metal such as aluminum, surface states and charge localization are important on specific crystalline faces. These states can affect the interface that forms between a metal and a semiconductor. For the Ga–GaAs interface investigated as the interface is formed, no Schottky barrier is found for Ga on p-type GaAs. Charge transfer from the surface As atoms to the Ga overlayers occurs, and some As migrates into the overlayer resulting in vacancies at the interface. Valence band changes with Ga coverage show that at least two occupied inteface states arise. These states, at −4.2 and −5.8 eV, fall within the gap in the surface Brillouin zone for projected bulk states. With alumimum an exchange reaction takes place, leaving an interfacial layer of AlAs and a GaAl alloy at the interface.