Lattice Dynamics of Thin-layered Semiconductor Superlattices

1.随着薄膜生长技术的发展，人们已经能够制备出新型的人造半导体超晶格。从晶格动力学的角度，拉曼散射实验揭示了新的性质，如光学声子限制，带折叠效应的声学色散，和界面模式的存在。在本研究计画中，我们借由计算拉曼光谱来探讨超晶格与薄表面层中的纵光学声子。我们还研究了声子通过电子-声子相互作用对二维电子性质的影响.结果与讨论我们对GaAs-Al_xGa_ As超晶格中LO声子的拉曼谱的研究结果<1-x>很好地描述了所观察到的拉曼分布。与受限LO声子相关的拉曼强度与构成超晶格的层的厚度有关。考虑到AlGaAs合金层中由于势涨落引起的声子阻尼的增加，讨论了声子阻尼对拉曼谱的重要影响。对P型GaAs的拉曼谱的分析也揭示了表面LO声子对整个谱的贡献。

1. IntroductionRecent advance of thin-film growth techniques has enable us to fabricate new man-made semiconductor superlattices. From lattice dynamical aspects, raman scattering experiments have revealed new properties, such as optical phonon confinement, zone-folding effects on the acoustic dispersion, and existence of the interface modes. In the present research program, we explore the longitudinal optical (lo) phonons in superlattices and thin surface layer by calculating the raman spectra. We also study the two-dimensional electronic properties which are affected much by phonons via electron-phonon interactions.2. Results and DiscussionsOur results for the Raman spectra by the LO phonons in GaAs-AL_xGa_<1-x>As superlattices provide a good description of the observed raman profile. The raman intensity associated with the confined lo phonons are related with the thickness of layers which constitute the superlattices. The important effects of phonon damping on raman spectra are discussed by taging into account the increase of damping due to potential fluctuations in alloy AlGaAs layer. Analysis of Raman spectra from P-type GaAs have also revealed the contribution from the surface LO phonons to whole spectra.