Characterization of structrual and optical properties of Si1 -xGex nanocrystal produced by laser-induced pyrolysis and by ion implantation

本项目的第一个目标是在原始条件下，通过尚未开发的方法，在气相中通过激光诱导硅烷(SiH4)和锗(GeH4)混合物的热解，以及(2)通过顺序离子(Si+和Ge+)注入和后处理，在气相中制备Si1？xGex纳米晶(Si1？xGex-NC)，或覆盖从x=0到x=1的整个范围的量子点。在工艺(1)中制备的纳米晶将在尺寸上进行选择并以薄膜的形式沉积在衬底上，而方法(2)中制备的纳米晶将被嵌入固体基质(主要是二氧化硅)中。应用这两种技术并改变工艺参数，可以制备出不同Si/Ge相对浓度和不同环境的Si1-xGex纳米晶，钝化氧化物壳层(1)或基质氧化物(2)。第二步，利用电子显微镜、红外光谱和拉曼光谱对量子点的结构和组成进行表征。我们将探索晶体结构如何随着尺寸和组成的变化而变化，以及是否可以观察到相变。最后，作为该提议最重要的目标，我们将研究Si1-xGex量子点的光致发光(PL)性质与尺寸和组成的函数关系。这些研究将解决这样一个问题：发光是否是量子限制系统中载流子辐射复合的结果，以及界面缺陷等其他机制在多大程度上起作用。量子限制的光致发光似乎最有趣，因为它允许通过改变大小来改变波长。在光电子学应用方面，我们的目标是验证理论预测的掺Ge后硅纳米晶的发光性能的改善。

The first objective of the present project is to produce Si1 ¿ xGex nanocrystals (Si1 ¿ xGex -nc), or quantum dots covering the entire range from x = 0 to x = 1, under original conditions and by means which have not yet been exploited: (1) in the gas phase by laser-induced pyrolysis of a mixture of silane (SiH4) and germane (GeH4), and (2) in matrices by sequential ion (Si+ and Ge+) implantation and postannealing. The nanocrystals prepared in process (1) will be selected in size and deposited on substrates in the form of thin films, whereas those prepared by method (2) will be embedded in solid matrices (mainly silica). Applying both techniques and varying the process parameters, Si1 - xGex nanocrystals with different Si/Ge relative concentrations and with various surroundings, passivating oxide shell in (1) or matrix in (2), will be produced. In the second step, the structure and composition of the quantum dots will be characterized by electron microscopy as well as IR and Raman spectroscopy. We will explore how the crystal structure varies with size and composition and whether phase transitions can be observed. Finally, constituting the most important objective of the proposal, we will investigate the photoluminescence (PL) properties of the Si1 - xGex quantum dots as a function of size and composition. The studies will address the question whether the PL results from radiative recombination of charge carriers in quantum-confined systems and to what extent other mechanisms such as interface defects are operative. Quantum-confined PL appears most interesting since it allows to vary the wavelength by varying the size. As far as optoelectronic applications are concerned, it is our aim to verify the improved PL properties of Si nanocrystals upon Ge-doping as predicted by theory.