Surface and bulk properties of GaAs(001) treated by selenium layers

The surface and bulk properties of GaAs(001) treated by means of different thicknesses of selenium layers has been studied. Insight into the mechanism of this type of surface treatment has been provided by surface-sensitive photoemission spectroscopy. It has been found that selenium deposited at room temperature on an arsenic-rich GaAs(001) surface initially reacts with the arsenic followed by the formation of a selenium overlayer. The experimental results show that the gallium and arsenic core levels shift only slightly during the deposition, suggesting that these atoms may reside in a well-defined local chemical environment through the observed thickness range of growth. An average value of 0.52 nm has been obtained for the inelastic scattering mean free path for 56 eV electron in the selenium layers. Heating the surface at 250°C causes the selenium to desorb and removes the selenium associated with the SeAs bonding. Following 500°C annealing all selenium has been found to be desorbed, resulting in a gallium-rich surface. There is no evidence for the formation of GaSe bonds during this process, unlike the situation when a hot GaAs surface is exposed to a selenium flux.