Showing papers by "Shin-ichi Nakashima published in 1998"
TL;DR: In this paper, a spectral lineshape analysis of the Raman scattering spectra from LO-phonon-plasmon coupled modes in n-type hexagonal GaN epitaxial layers is presented.
Abstract: Raman scattering spectra from LO-phonon-plasmon coupled modes in n-type hexagonal GaN epitaxial layers have been measured in detail for different carrier densities in n=10{sup 17}-10{sup 18} cm{sup -3}. Both the upper and lower branches of the coupled modes were clearly observed, showing striking changes in lineshape and peak frequency with the carrier density. A spectral lineshape analysis shows that n-type GaN belongs to a system of under-damped plasmon satisfying {omega}{sub P}{tau}>or{approx}1, where {omega}{sub P} and {tau} are the plasmon frequency and scattering time, respectively. This is in contrast with other wide band-gap semiconductors such as SiC, which shows clearly the character of over-damped plasmon, {omega}{sub P}{tau}<1. A measurement of spatial distribution of carrier density in epitaxial layers is also presented for an application of the coupled-mode analysis. (orig.) 9 refs.
40 citations
TL;DR: In this paper, the authors studied the Raman spectra from p-type GaN in the hole density range of 5×1016 −1×1018 cm−3.
Abstract: Raman spectra from p-type GaN have been systematically studied in the hole density range of 5×1016–1×1018 cm−3. Contrary to the case of n-type samples, spectral profiles of the LO-phonon-plasmon coupled mode in p-type show no remarkable change with the hole density. Thus, precise evaluation of electrical transport parameters such as carrier density and mobility from the coupled mode profile is difficult. However, a continuum band has been observed in the low-frequency range of the spectra, becoming intense with the increase of the hole density. This band has been attributed to the inter-valence-band transition of holes, and the intensity can be used as a good measure of the hole density.
39 citations
TL;DR: In this paper, it was shown that lateral distributions of carrier density and mobility in epitaxial layers can be obtained by analyzing the coupled-mode line shape of the LO-phonon plasmon coupled mode.
25 citations
16 citations
TL;DR: In this article, the dominant phase can be estimated by the observation of the transverse-optic (TO) phonon band spectra, which may suggest a two-mode behavior for the TO mode of mixed crystals.
11 citations
TL;DR: In this article, coherent optical phonons were detected in the reflectivity signal in both the normal and the CDW states. And they concluded that the generation of these coherent phonon modes are closely related to the CDw state.
Abstract: The charge-density-wave ~CDW! phase transition in h-Mo4O11 is studied by femtosecond time-resolved reflection. We observed coherent optical phonons in the reflectivity signal in both the normal and the CDW states. Below the transition temperature Tc1 , six vibrational modes were clearly detected. Four of them, centered at 64, 78, 85, and 98 cm, were enhanced below Tc1 . We conclude that the generation of these coherent phonon modes are closely related to the CDW state. @S0163-1829~98!50140-3#
6 citations
6 citations
6 citations
TL;DR: In this paper, the authors proposed that the processes taking place at the surface of NbSe2 are due to mechanical and chemical interactions that unsaturated bonds which are present in surface defects and step edges have with the environment and the tip.
5 citations
TL;DR: In this article, the coherence of coherent phonons in time domain was examined using a double-pulse excitation technique using a reflection type pump-probe technique and discussed the phonon dynamics.
Abstract: Coherent phonons can be generated in solids by ultra-short pulse laser excitation. Here we report observation of coherent phonon oscillations in the time domain using reflection type pump-probe techniques and discuss the phonon dynamics. An A1g phonon mode was observed for Bi, showing an exponentially decaying oscillation. Temperature dependence of the phonon frequency and the decay rate agrees with the result of Raman measurements. This indicates that the decay process of the coherent phonon is dominated by an anharmonic decay route of energy relaxation. The coherence of phonons in time domain was examined using a double-pulse excitation technique. The oscillation amplitude of the A1g mode in Bi enhances when the pulse separation time is equal to the period of the phonon oscillation, and vanishes when the separation time is adjusted to half integral multiples of the period. We present furthermore the results on coherent folded acoustic modes in GaAs/AlAs superlattices.
4 citations