SURFACE-STRUCTURE OF SE-TREATED GAAS(001) FROM ANGLE-RESOLVED ANALYSIS OF CORE-LEVEL PHOTOELECTRON-SPECTRA

Angle-resolved core-level photoelectron spectroscopy using a monochrom atized synchrotron radiation source was used to study the structure of the Se-treated GaAs(001) surface. Depth profiling was achieved by var ying the photoelectron angle with respect to the sample surface. The S e 3d spectrum was found to consist of two components. The higher-kinet ic-energy component is assigned as the surface-sensitive component, wh ich is opposite to the conventional assignment based on Ga coordinatio n. The intensity ratios of the two Se components are calculated with a layer attenuation model, and the polar angle dependence shows that th e two components cannot simply be assigned as ''surface'' and ''inner' ' Se but are two different chemical states that exist at both the firs t and second Se layers, with only one chemical state existing at the t hird Se layer. Based on these results, we derived a Ga-vacancy zinc-bl ende structure where the first Ga layer has a vacancy occupancy of app roximately 25%.