Analyzing the Growth Mechanism of Ge Dots on Si Patterned Substrate with Chemical Potential Theory
Date Issued
2010
Date
2010
Author(s)
Chen, Shih-Ta
Abstract
The theory and experiment of quantum dot are currently an interesting issue. Since its size of the three dimensions is less than the electron wavelength, electron movement is restricted in all direction, and the quantum confinement effect is more significantly. There are many advantages on the fabrication of germanium quantum dots by the self-assembly method, diversity, simplicity and low cost in fabrication procedure. The precise positioning of the quantum dots is required for its application on electronic and optical devices. So using the silicon patterned substrates to control the position of germanium quantum dots is the best choice.
This thesis made an effort to study what the impact of the chemical potential in the Si/Ge interfacial system on the germanium dots’ growth mechanism on the silicon patterned substrate. First, I studied the physical meaning of the chemical potential, and then I gave a quantitative description for chemical potential. Next I fabricated the one-dimensional grating and simulated it by the chemical potential model. We found out that the width of the trench will affect the distribution of the chemical potential in grating structure. And then I introduced the mathematical concept of how to tackle the curvature in two-dimensional case, so our simulation can be extended to two-dimensional system. Then I simulated the two-dimensional hole array structure and found that the period of the in-situ heat treatment in the fabrication process, the hole size, pitch, shape and the sidewall of the hole array will influence the distribution of the chemical potential.
Based on the simulation result of the chemical potential, I can get a conclusion that the decreasing of the pitch and the smoothen of the sidewall of the hole array will lower the chemical potential barrier around the hole. The germanium dots will locate inside the hole. Decreasing the hole size and the period of the in-situ heat treatment before the epitaxy will get an only one chemical potential minimum inside the hole. The germanium dots will position in the hole center.
Besides, I used the electron beam lithography system and the ultra high vacuum chemical vapor deposition system in experiment to fabricate the samples according to the above conditions. The result in the experiment is agreed to the chemical potential simulation.
So the simulation by the chemical potential model can precisely predict the position of the germanium quantum dots on the silicon patterned substrate.
Subjects
Chemical potential model
surface energy
strain energy
self-assembled quantum dots
S-K growth model
Type
thesis
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