Temperature dependence of energy gap in GaN thin film studied by thermomodulation

The thermomodulation spectrum from metal organic chemical vapor deposition grown GaN has been measured in the temperature range of 20–310 K. A theoretical model is established to explain the spectrum by considering the modulation of dielectric constant and epilayer thickness. It is found that the latter is especially important for a material system with a large difference in refractive indices between the epilayer and the substrate. The band gap energy and broadening parameter are determined using a lineshape analysis. Varshni coefficients of the energy gap are determined. The temperature dependence of broadening parameter is also measured.