DENSITY-OF-STATES, HYBRIDIZATION, AND BAND-GAP EVOLUTION IN ALXGA1-XNALLOYS

The electronic structure of the wurtzite AlxGa1-xN alloy system has be en studied for numerous values of Al concentration x ranging from 0 (p ure GaN) to 1 (pun AlN). The occupied and unoccupied partial density o f states was measured for each alloy using synchrotron radiation excit ed soft x-ray absorption and emission spectroscopies. High-resolution x-ray emission spectroscopy allowed the motion of the elementally reso lved bulk valence-band maximum to be measured as a function of Al conc entration. Using this technique we estimate that the value of the band -gap bowing parameter for AlxGa1-xN is zero. Furthermore, the x-ray em ission spectra revealed resonantlike emission at approximately 19 eV b elow the GaN valence-band maximum. By measuring the intensity of this feature as a function of Ga content we prove conclusively that this em ission arises from hybridization of N 2p and Ga 3d states. Finally, we find that the N K- and Al K-absorption spectra depend strongly on the photon angle of incidence with respect to the surface normal. We expl ain this in terms of orbital anisotropy in AlxGa1-xN.