Band-gap evolution, hybridization, and thermal stability ofInxGa1−xNalloys measured by soft X-ray emission and absorption

Abstract

The electronic structure of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ 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 ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloy system, which observed a linear valence-band shift through the series $(0<~x<~1).$ For ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ the valence band exhibits a large shift between $x=0$ and $x=0.1$ with minimal movement thereafter. We also report evidence of In $4d--\mathrm{N}$ $2p$ and Ga $3d--\mathrm{N}$ $2p$ hybridization. Finally, the thermal stability of an ${\mathrm{In}}_{0.11}{\mathrm{Ga}}_{0.89}\mathrm{N}$ 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.