Angle-resolved core-level photoelectron spectroscopy using a monochromatized synchrotron radiation source was used to study the structure of the Se-treated GaAs(001) surface. Depth profiling was achieved by varying the photoelectron angle with respect to the sample surface. The Se 3d spectrum was found to consist of two components. The higher-kinetic-energy component is assigned as the surface-sensitive component, which is opposite to the conventional assignment based on Ga coordination. The intensity ratios of the two Se components are calculated with a layer attenuation model, and the polar angle dependence shows that the two components cannot simply be assigned as ‘‘surface’’ and ‘‘inner’’ Se but are two different chemical states that exist at both the first and second Se layers, with only one chemical state existing at the third Se layer. Based on these results, we derived a Ga-vacancy zinc-blende structure where the first Ga layer has a vacancy occupancy of approximately 25%.

• Received 1 June 1993

DOI:https://doi.org/10.1103/PhysRevB.48.4956