Effect of electron distribution in InN films on infrared reflectance spectrum of longitudinal optical phonon-plasmon interaction region

The infrared reflectance spectra of InN/GaN structures are analyzed in two energy regions for higher and lower energy branches of the longitudinal optical phonon-plasmon coupled modes. For samples with smaller residual electron density than 5x10(17) cm(-3) and the film thickness of 0.7-4 mu m, the spectra down to 200 or 250 cm(-1) shows the existence of the electron accumulation with sheet electron density of 10(13) cm(-2) in the vicinity of the InN/GaN-interface. The effect of the surface electron accumulation on the spectra is not identified, which is possibly caused by the small mobility of the order of 10 cm(2)/V s or less for the surface electrons. The electron density of the inside bulk region is obtained with account of this interface accumulation. However, for samples with higher electron density and thickness of several micrometers a model with uniform electron density well reproduce the experimental spectra. With this spectrum fitting we extract the electron properties inside the bulk region for samples with the thickness of about 700 nm or larger. (c) 2008 American Institute of Physics.