X-ray spectroscopic studies of the bulk electronic structure of InGaN alloys

Synchrotron radiation excited soft x-ray emission and soft x-ray absorption spectroscopies are applied to the study of the electronic structure of In_xGa_1-xN alloys with (0 ≤ x ≤ 0.29). The elementally resolved partial density of states of the valence and conduction bands may be measured using these spectroscopies. The x-ray absorption spectra indicate that the conduction band broadens considerably with increasing indium incorporation. The band gap evolution as a function of indium content derives primarily from this broadening of the conduction band states. The emission spectra indicate that motion of the valence band makes a smaller contribution to the evolution of the band gap. This gap evolution differs from previous studies on the Al_xGa_1-xN alloy system, which observed a linear valence band shift through the series (0 ≤ x ≤ 1). Instead in the case of In_xGa_1-xN the valence band exhibits a significant shift between x = 0 and x = 0.1 with minimal movement thereafter. Furthermore, evidence of In 4d -N 2p and Ga 3d - N 2p hybridisation is reported. Finally, the thermal stability of an In_0.11Ga_0.89N film was investigated. Both emission and absorption spectra were found to have a temperature dependent shift in energy, but the overall definition of the spectra was unaltered even at annealing temperatures well beyond the growth temperature of the film.