小尺寸Si/Ge量子点内应变和组分的拉曼光谱表征

本文详细地研究了原始生长和退火处理后的Si/Ge量子点的拉曼光谱。我们观测到了Si/Ge量子点的一系列本征的拉曼振动模以及Ge-Ge模的LO和TO声子峰间4.2cm-1的频率劈裂。通过这些参数,我们自洽地确定了原始生长的平面直径为20nm和高为2nm的Si/Ge量子点内Ge的平均组分为80%,平均应变为-3.4%。分析清楚地表明了这种小尺寸的Si/Ge量子点内的应变仍遵从双轴应变,并且应变的释放主要由量子点和Si隔离层间Si-Ge原子互扩散决定。

Raman Characterization of Strain and Composition in Small-sized Self-assembled Si/Ge Dots

A detailed Raman characterization of the structural properties of as-grown and annealed self-assembled Si/Ge dot multilayers is reported in this paper. Several new modes in as-grown or annealed Si/Ge dots and a frequency splitting of 4.2 cm~(-1) between LO and TO Ge-Ge modes in as-grown Si/Ge dots are observed in Raman spectra. An average Ge content of 0.8 and lateral strain of -3.4% are consistently obtained from these spectral features for as-grown Si/Ge dots with a lateral size of about 20 nm and a height of about 2 nm. It suggests that a certain amount of intermixing between Si spacer layers and Si/Ge dots takes place for the Si/Ge dot multilayers. The results show that the LO-TO frequency splitting of the Ge-Ge mode and the frequencies of the Ge-Ge and Ge-Si modes can be used as an efficient way to determine the average strain and composition in uncorrelated small-sized Si/Ge dot multilayers in which the mean strain field is close to the biaxial case.