The initial oxidation features of (NHn)zS ,-treated GaAs surfaces has been investigated by photoelectron spectroscopy in order to correlate the photoluminescence (PL) degradation eaused by oxidation with band bending and surface chemical bonding changes. Direct eorrelation between the drastical upward band bending caused by oxidation and PL degradation is observed. It is also found that the S-passivated surfaee inhibits oxidation reaction, and that the underlying GaAs is oxidized leaving the surface GaS layer unoxidized.
The passivation of GaAs(100) by Se has been achieved in a controlled manner. Results provided by synchrotron radiation photoelectron spectroscopy show that the extent of Se bonding to As and degree of band bending can be systematically controlled by varying the GaAs substrate temperature during Se exposure. Furthermore, the formation of Ga vacancies is also found to depend on substrate temperature.
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 surfacesensitive 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%.
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