Band-gap evolution, hybridization, and thermal stability of In_xGa_1-xN alloys measured by soft X-ray emission and absorption

The electronic structure of In_xGa_1-xN alloys with (0≤x≤0.3) has been studied using synchrotron radiation excited soft x-ray emission and absorption spectroscopies. These spectroscopies allow the elementally resolved partial density of states of the valence and conduction bands to be measured. The x-ray absorption spectra indicate that the conduction band broadens considerably with increasing indium incorporation. The evolution of the band gap 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). For In_xGa_1-xN the valence band exhibits a large shift between x=0 and x=0.1 with minimal movement thereafter. We also report evidence of In 4d-N 2p and Ga 3d-N 2p hybridization. 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.