Mechanical and Optoelectronic Properties of Self-Assembled Quantum Dots
Date Issued
2006
Date
2006
Author(s)
Lin, Tzy-Rong
DOI
zh-TW
Abstract
The coupling mechanical strain and opto-electronic properties in self-assembled quantum-dot nanostructures are studied. A model, based on the theories of linear electricity and k•p, is developed to analyze chemical composition effects, shape effects, size effects, and multiple layers effects on mechanical and opto-electronic properties of the self-assembled InGaAs /GaAs quantum dots by means of finite element analysis.
At first, the strain fields of surface quantum dots induced by mismatch of lattice constants between the quantum-dot material and substrate material are analyzed. For cases of indium concentrations , The calculated results of strain relaxations have good agreement with what are taken experimentally through HREM imaging by others. On the other hand, a new two-step model is proposed to analyze strain fields of buried quantum dots. The model takes into account of the sequence of the fabrication process of buried quantum dots. Then strain-induced as well as piezoelectric effects are considered by modifying the carrier confinement potential in Schrödinger equation. The strain-induced potential is determined from deformation potential theory. Also, the piezoelectric potential is analyze by solving Poisson’s equation. After that, the steady-state effective-mass Schrödinger equation is adopted to find confined energy levels as well as wave functions both for electrons and holes of the quantum-dot nanostructures. Finally, energies of interband optical transitions are acquired in numerical experiments.
The numerical results show that the strain field from this new two-step model is significantly different from models where the sequence of the fabrication process is completely omitted. The calculated optical wavelength from this new model agrees well with previous experimental photoluminescence data from other studies. Piezoelectric effect, on the other hand, splits the p-like degeneracy for the electron first excited state about 1~7 meV, and leads to anisotropy on the wave function. The effect was also experimentally observed through magnetotunneling spectroscopy by others.
Subjects
自聚式量子點
應變場
壓電效應
有限元素法
薛丁格方程式
self-assembled quantum dot
strain field
piezoelectric effect
Schrodinger equation
Type
thesis
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