Showing papers by "Shin-ichi Nakashima published in 2008"
TL;DR: In this article, the authors characterized GaN crystals with various dislocation densities by micro-Raman spectroscopy and examined defects and strain for the GaN layer through measurements of the Raman shift and the width of the TO phonon bands.
Abstract: We characterized GaN crystals with various dislocation densities by micro-Raman spectroscopy Defects and Strain for the GaN layer were examined through measurements of the Raman shift and the width of the TO phonon bands The broadening of Raman bands in GaN crystals occurred as the dislocation density increased The up-shift of the peak frequencies corresponding to compressive strain was observed for the heteroepitaxial samples grown by MOCVD and MBE The in-plane distribution of defects and strain in epilayers with various dislocation densities was also examined by Raman mapping The Raman maps showed that the examined phonon frequency and band width in samples fluctuated spatially The increase of dislocation density in GaN epilayers induced not only the broadening of Raman bands but also increase of fluctuation (© 2008 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
19 citations
TL;DR: In this paper, the free carrier concentration of n-4H-SiC was deduced by Raman spectroscopy using LO phonon plasmon coupled (LOPC) modes as a monitor band.
Abstract: The free carrier concentration of n-4H-SiC was deduced by Raman spectroscopy using LO phonon plasmon coupled (LOPC) modes as a monitor band. We could determine the free carrier concentration from the reading of the peak frequency of the LOPC mode in the concentration range from 1019 down to 1016cm−3. The damping of LO phonons was evaluated as a function of the carrier concentration. Line shape analysis of the LOPC mode revealed that the damping of the LO phonon deduced from this analysis is sensitive to charged defects including ionized impurities.
17 citations
TL;DR: In this article, the authors characterized the 4H and 6H-SiC bulk crystals with graded doping and epitaxial films with various carrier densities by Raman scattering spectroscopy.
Abstract: We characterized the 4H- and 6H-SiC bulk crystals with graded doping and epitaxial films with various carrier densities by Raman scattering spectroscopy. Electrical properties such as free carrier density were examined for the SiC crystals through Raman measurements of the A1 LO-phonon plasmon coupled (LOPC) mode and its line shape analysis. The peak frequency and band width of LOPC mode varied with carrier density in the range from 1016 to 1019 cm-3. The line shape analysis revealed that the carrier density in the SiC crystals can be simply estimated from measured frequency shift of LOPC mode for 4H- and 6H-SiC crystals.
5 citations
TL;DR: In this article, the authors characterized the HVPE grown freestanding GaN crystals with various shallow impurity concentrations by Raman scattering spectroscopy and showed that the carrier density in the GaN crystal can be simply estimated from measured frequency shift of LOPC mode.
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.
1 citations