STUDY OF RAMAN-SPECTRA OF ZNSE-ZNTE STRAINED LAYER SUPERLATTICES

The Raman spectra of the II-VI wide band-gap compound ZnSe-ZnTe semiconductor strained-layer superlattices have been studied. The relations between the Raman shifts of the longitudinal optical phonon modes and the superlattice-structure parameters have been determined. When the layer thickness exceeds 40 angstrom, the change of the LO phonon-mode frequency shifts with the layer thickness is minimal, whereas when the layer thickness is smaller than 40 angstrom, great shifts have been observed. We estimate that the critical thickness of ZnSe-ZnTe SLS is about 40 angstrom. We have also found that the shifts induced by strain are much larger than the red shifts due to confinement.

NEAR-RESONANCE RAMAN-SCATTERING OF LONGITUDINAL OPTICAL PHONON MODES AND INTERFACE MODES IN GAAS/ALAS SUPERLATTICES

The near-resonance Raman scattering of GaAs/AlAs superlattices is investigated at room temperature. Owing to the resonance enhancement of Frohlich interaction, the scattering intensity of even LO confined modes with A1 symmetry becomes much stronger than that of odd modes with B2 symmetry. The even modes were observed in the polarized spectra, while the odd modes appear in the depolarized spectra as in the off-resonance case. The second-order Raman spectra show that the polarized spectra are composed of the overtone and combinations of even modes, while the depolarized spectra are composed of the combinations of one odd mode and one even mode. The results agree well with the selection rules predicted by the microscopic theory of Raman scattering in superlattices, developed recently by Huang and co-workers. In addition, the interface modes and the combinations of interface modes and confined modes are also observed in the two configurations.

RAMAN-SCATTERING BY LO PHONONS IN (GAAS)N1/(ALAS)N2 ULTRATHIN-LAYER SUPERLATTICES

Raman spectra of (GaAs)n1/(AlAs)n2 ultrathin-layer superlattices were measured at room temperature and under off-resonance conditions. The experimental results show that there are two effects in ultrathin-layer superlattices: the confinement effect of LO phonons and the alloy effect. It is found that the relative intensity of the disorder-activated TO mode can give a measure of the alloy effect. The Raman spectra of one-monolayer superlattices measured in various scattering configurations are very similar to those of the Al0.5Ga0.5As alloy, and thus the alloy effect is prominent. However, in the case of monolayer number n greater-than-or-equal-to 4, the confined effect is prominent, while the alloy effect is only shown as an interface effect.

Absorption and Raman spectra of Se-8-ring clusters in zeolite 5A

Samples with different weight ratio of Se to zeolite 5A (Se composition) have been prepared by loading Se into the cages of zeolite 5A and the measurements of the absorption and Raman spectra have been carried out for the prepared samples. The measured absorption edges of the samples close and blue shifted to the value for monoclinic Se containing Se-8-ring, suggesting the formation of Se-8-ring clusters dagger in the cages. The continuous and broadening features of the absorption spectra are interpreted by the strong electron-phonon coupling in Se-8-ring clusters. The sample with high Se composition has a red shift of the absorption band edge relative to the samples with less Se composition. It is tentatively attributed to the reason that with different Se composition, single Se-8-ring clusters and double Se-8-ring clusters are formed in the cages of zeolite 5A. A single broad band at about 262 cm(-1) is observed in the Raman spectra, that gives the further support of the formation of Se-8-ring clusters. Copyright (C) 1996 Elsevier Science Ltd

A RESONANT RAMAN-STUDY ON PHONONS IN GAINAS/ALINAS MULTIPLE-QUANTUM WELLS

The LO phonon modes in the barrier layers of a GaInAs/AlInAs multiple quantum well structure are investigated by resonance Raman scattering (RRS), the excitation laser photon energy tuned to resonate with the above barrier interband transition energy. The resonance enhancement of LO phonon peaks are shown to be caused by Frohlich electron-phonon interaction. The pressure-dependent profiles for both AlAs-like (LO(2) mode) and InAs-like (LO(1) mode) Raman peak intensities are well fitted by the Gaussian lineshape. The shift between these two profiles can be explained by the outgoing RRS mechanism, providing information on the pressure-induced shift of the excitonic transition energy. The amplitude ratios of the two profiles are close to 1, showing a well defined two-mode behavior and the nearly equal polarizability for Al-As and In-As bonds in AlInAs alloy.

GaMnAs的Raman光谱研究

报道了磁性半导体材料GaMnAs的拉曼光谱，发现其空穴等离子体激元与LO声子振动耦合形成的CPLP模具有类LO模的偏振特性．随着Mn组分的增加，CPLP模的拉曼频率红移，通过CPLP模与耗尽层中未屏蔽的LO模的强度比计算了合金中的空穴载流子浓度．发现空穴浓度随Mn组分的增加而迅速增加．测量了不同温度下GaMnAs合金的拉曼光谱,证实合金中空穴浓度随温度的增加而增加．