Energy bandgap bowing of InAlN alloys studied by spectroscopic ellipsometry

InxAl1-xN films were heteroepitaxially grown on AlN/Al2O3 (0001) templates by molecular beam epitaxy. The compositions studied spanned the whole ternary range. The complex dielectric function of the films was investigated by variable angle spectroscopic ellipsometry in the energy range from 0.55 to 6 eV. The energy bandgap bowing parameter was found to strongly depend on composition, monotonically increasing with decreasing InN mole fraction. This behavior is in agreement with theoretical predictions of large charge transfer contributions to bandgap bowing. (C) 2008 American Institute of Physics.