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和尚未开发的方法下生产Si1¿xGex纳米晶体（Si1¿xGex -nc），或覆盖从x = 0到x = 1的整个范围的量子点：(1)在气相中通过激光诱导裂解硅烷（SiH4）和锗烯（GeH4）的混合物，以及(2)在基质中通过顺序离子（Si+和Ge+）注入和后退火。在工艺(1)中制备的纳米晶体将选择尺寸并以薄膜形式沉积在衬底上，而通过方法(2)制备的纳米晶体将嵌入固体基质（主要是二氧化硅）中。应用这两种技术和改变工艺参数，将生产出具有不同Si/Ge相对浓度和不同环境的Si1 - xGex纳米晶体，钝化氧化物壳(1)或基质(2)。在第二步，量子点的结构和组成将通过电子显微镜以及红外和拉曼光谱进行表征。我们将探讨晶体结构如何随尺寸和组成而变化，以及是否可以观察到相变。最后，作为本文最重要的目标，我们将研究Si1 - xGex量子点的光致发光（PL）特性与尺寸和组成的关系。这些研究将解决PL是否来自量子受限系统中载流子的辐射重组以及其他机制（如界面缺陷）在多大程度上起作用的问题。量子受限PL看起来最有趣，因为它允许通过改变尺寸来改变波长。就光电应用而言，我们的目标是验证ge掺杂后Si纳米晶体的PL性能是否如理论预测的那样得到改善。

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.