Raha Sreyan, Biswas Subhajit, Doherty Jessica, Mondal Prasanna Kumar, Holmes Justin D, Singha Achintya
Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009, India.
School of Chemistry & Advanced Materials and Bioengineering Research (AMBER) Centre, University College Cork, Cork T12 YN60, Ireland.
Nanoscale. 2022 May 19;14(19):7211-7219. doi: 10.1039/d2nr00743f.
Alloying group IV semiconductors offers an effective way to engineer their electronic properties and lattice dynamics. The incorporation of Sn in Ge permits a transition from an indirect to a direct bandgap semiconductor. Here, by combining polarization, laser power-dependent and temperature-dependent micro-Raman spectroscopy we explore the full lattice dynamics of GeSn ( = 0.01, 0.06 and 0.08) alloy nanowires. In the high Sn content samples ( ≥ 0.06), a low-frequency tail and a high-frequency shoulder are observed which are associated with the F optical phonon mode of Ge (Ge-Ge mode). The new modes are assigned to the stretching of Ge-Ge bonds due to Sn-induced lattice relaxation and compression, respectively. The symmetry of the observed Raman modes has been studied by polarization-dependent Raman scattering. Nonlinear fitting of the laser power-dependent intensity of the high-frequency Ge-Ge mode in the GeSn alloy nanowires with = 0.06 and 0.08 suggests the activation of a third-order stimulated Raman scattering process, due to the high intensity localized electric field surrounding the Sn clusters. Finally, from the temperature-dependent Raman study, we have estimated the isobaric Grüneisen parameters for all the observed modes.
对IV族半导体进行合金化是一种调控其电子特性和晶格动力学的有效方法。在锗中掺入锡可使半导体从间接带隙转变为直接带隙。在此，我们结合偏振、激光功率依赖和温度依赖的显微拉曼光谱，探究了GeSn（x = 0.01、0.06和0.08）合金纳米线的完整晶格动力学。在高锡含量样品（x≥0.06）中，观察到一个低频尾部和一个高频肩部，它们与锗的F光学声子模式（Ge-Ge模式）相关。新的模式分别归因于锡诱导的晶格弛豫和压缩导致的Ge-Ge键的拉伸。通过偏振依赖拉曼散射研究了所观察到的拉曼模式的对称性。对x = 0.06和0.08的GeSn合金纳米线中高频Ge-Ge模式的激光功率依赖强度进行非线性拟合，表明由于锡团簇周围的高强度局域电场，激活了三阶受激拉曼散射过程。最后，通过温度依赖拉曼研究，我们估算了所有观察到的模式的等压格林爱森参数。
