Alloy composition fluctuation and band edge energy structure of In-rich In_xGa_(1-x)N layers investigated by systematic spectroscopy

摘要

After the finding of the bandgap energy of InN as less than 1 eV, the re-examination of the bandgap of InGaN alloys and its bowing parameter is an issue of interest. We study the absorption spectra of In-rich InGaN layers by taking account of the Burstein-Moss effect and bandgap renormalization with the analysis of photoluminescence and infrared reflectance spectra. We find the far larger broadening of optical transition and lattice vibration energies than those expected from the alloy composition fluctuation based on the x-ray diffraction patterns. We estimate that local potential fluctuation by the alloy composition fluctuation give rise to the strong localization of carriers and relaxation of the momentum conservation rule in optical transition. The average bandgap energies of the films show the bowing parameter less than 1.4 eV; the value down to 0.7 eV is possible.