Photoelectron Spectroscopy Studies of III-V Semiconductor Systems

Doctoral thesis, 2001

Photoelectron spectroscopy has been used as a main tool to study a number of III-V semiconductor surfaces. This thesis includes studies of a surface reaction, As/InP(110), thin heteroepitaxial layers, InAs on GaAs(111)A and GaAs on AlAs(100), and a diluted magnetic semiconductor, Ga1-xMnxAs. Also GaAs prepared under similar low temperature MBE conditions as GaMnAs has been studied. In addition, a report on core-exciton-mediated resonant photoemission from some of these systems is included. In a core-level and valence-band investigation of As/InP(110) it was shown that an exchange reaction between adsorbed As and substrate P takes place at elevated temperatures, irreversibly changing the surface conditions. A systematic study of valence-band spectra from ultra-thin InAs/GaAs(111)A and GaAs/AlAs(100) films was aimed at following the gradual development of bulk-character in the overlayer electronic structure. Thickness-dependent modi-fications of the valence-band spectra show that the interface region in effect displays alloy-like properties extending 2-4 nm, even though the interface is geometrically abrupt. This is interpreted as an effect of electronic states tailing across the interface. Valence-band spectra from LT-GaAs (T<300 oC) exhibit small differences from ordinary GaAs, indicating modifications in the photoemission properties. The Ga 3d signal is also found to contain a LT-characteristic feature, which is interpreted as an effect of AsGa antisites. The first photoemission results from an extensive study of in situ MBE-grown Ga1-xMnxAs with varying Mn concentrations are also presented. The Mn-induced changes in the valence-band are shown to depend strongly on the Mn concentration as do the relative position of the Fermi level. Interestingly, the Fermi level moves down to the VBM for a Mn concentration range (3.5-5%) corresponding to that where metallic conductivity and maximum Curie temperatures have been reported. Migration enhanced epitaxy (MEE) is demonstrated to enable incorporation of at least 10% Mn in LT-GaAs. The Ga0.9Mn0.1As sample displays higher Curie temperatures than samples with 6-7% Mn, breaking the negative trend of diminishing TC for x>0.05.