Raman Scattering Analysis of Electrical Property and Crystallinity in Freestanding GaN Crystals with Various Impurity Concentrations

Abstract

We characterized the HVPE grown freestanding GaN crystals with various shallow impurity concentrations by Raman scattering spectroscopy. Electrical properties such as free carrier density were examined for the GaN crystals through Raman measurements of the A1 LO-phonon plasmon coupled (LOPC) mode and its line shape analysis. The asymmetric broadening and the up-shift of the LOPC band were clearly observed as the carrier density increased from 1017 to 1019 cm-3. The line shape analysis revealed that the carrier density in the GaN crystals can be simply estimated from measured frequency shift of LOPC mode. The variations of the width for TO phonon bands were also observed in this carrier density range. The band widths were slightly increased by 0.2 cm-1 as the impurity concentration increased from 1018 to 1019 cm-3 in samples with low dislocation density.