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Temperature and composition dependence of the band gaps of Ga$_{1-x}$In$_x$N alloy: a first-principles study based on the virtual crystal approximation

We report on the structural, electronic and vibrational properties of the Ga$_{1-x}$In$_x$N alloy using virtual crystal approximation (VCA) from first-principles. A band gap bowing parameter of 3.85 eV is obtained with the TB09 functional. Phonon density of states shifts to lower frequency as the In content is increased. However, VCA ignores disorder effect and is therefore unable to describe the broadening of the phonon spectra upon alloying. The role of electron-phonon interaction in the temperature dependence of the band gap is also studied for GaN, InN and their alloy Ga$_{1-x}$In$_x$N. The calculated zero-point motion renormalization and the fitted Varshni parameter over the entire composition range are discussed.