The Characteristics of Silicon and Silicon-Germanium Alloy Quantum Dots Prepared by Thermal Evaporation Method

• Main Authors: Yu-Cheng Liao, 廖友誠
• Other Authors: Si-Chen Lee
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/27183000835210473029

碩士 === 國立臺灣大學 === 電機工程學研究所 === 88 === Spherical silicon (Si), germanium (Ge), and silicon-germanium (SiGe) alloy quantum dots have been grown by thermal evaporation method. This is the first time that SiGe quantum dots are synthesized by this method. The structural and optical properties of these dots are studied in detail. It is found that the size of the Si quantum dots and their variation become larger while the growth pressure increases. The particle size is found to be in the range from 4 to 50 nm. By using transmission electron microscopy (TEM) and Raman spectroscopy, a critical size about 4 nm for the Si nanoparticles is found, while the particle is smaller than 4 nm, an amorphous Si film instead of quantum dots is deposited. But when the particle size exceeds 4 nm, the stable Si nanoparticles appear. For Ge nanoparticles, similar phenomenon is also observed. These are possibly originated from the lattice expansion effect which is more serious while the dots are smaller. A growth model for explaining the critical phenomenon is proposed. An abnormality observed in the transmission spectra of the deposited film can be well explained by this model. For the SiGe alloy quantum dots, it is found that the core of the dots is a single crystal and the composition of these dots could be adjusted by varying the evaporation rate of constituent elements. The transmission electron diffraction (TED) pattern and Raman spectra are used to estimate the composition of the dots. Besides, the optical transmission spectra of these dots are measured and explained in this study.