Performance Investigation And Structure Optimization Of The Semiconductor Microstructure

With the rapid development of information technology, photoelectric device need more higher performance materials. However, as the fabrication technique and microtechnique improved, people began to expand the research scope to nano-materials from macroscopic materials. The semiconductor microstructure materials became an essential part of the new generation optoelectronics devices and materials gradually due to its unique photoelectric properties. The emergence of such new structure makes it possible for all optical processing and miniaturization of photonic devices, which will be the key factor of promoting the rapid development of information technology.The work in this thesis is supported by the National Natural Science Foundation of China (Grant No.60971068) and the National High Technology Research and Development Program of China (Grant No.2009AA03Z405), and focus on the performance investigation and structure optimization of the semiconductor microstructure (quantum dot, nanowire and photonic crystal structure). The main achievements of this thesis are as follows:1. Calculation on the equilibrium composition of the quantum dot. We combine the method of moving asymptotes and finite element method to develop a new faster method for optimization the equilibrium composition of the quantum dot. Based on this method, we calculate the composition of the dome shaped GexSi1.x/Si quantum dot at different temperature and investigate the physical mechanism of this process. In addition, we study the influence of the composition optimization on the critical size of the shape transition for pyramid shaped GexSi1-x/Si quantum dot.2. Search on the influence of adjacent quantum dot on the composition distribution and the optimal deposition position of the quantum dot in the quantum dot multilayer system. Based on the method of composition calculation, we investigate the effect of near laterally and vertically neighboring quantum dots on the composition of uncapped InxGa1-xAs/GaAs quantum dots, and study the relationship between the coupled stress field and composition distribution. We also study the affecting factors of the alignment position of the quantum dot in InAsxP1-x/InP quantum dot multilayer system by using the least energy principle.3. Research on the critical size of the substrate mesa for single quantum dot growth. Also based on the composition calculation method, we can obtain the minimum Gibbs free energy of the quantum dot system to study the deposition site and shape transition of the quantum dot on the substrate mesa. Calculating the free energies of the systems with single quantum dot on the mesa and two quantum dot on the mesa, to find out the critical size of the substrate mesa for single quantum dot growth by using the least energy principle.4. Optimization the top structure of the nanowire for improving the efficient of the photon collection. We construct a three dimensional nanowire finite element model and optimize the top profile of the nanowire by employing the geometry projection method for maximum photon collection efficiency. After optimization, we find that the nanowire with cambered top has stranger forward emission than that for cylindrical top, which is convenient for photon collection.5. Optimization of a two dimensional photonic crystal for the largest absolute band gap. We optimization the two dimensional photonic crystal structure by employing the geometry projection method which can overcome the drawback of large calculation quantity in traditional topology optimization. After optimization, we obtain a new photonic crystal structure with absolute band gap about0.1735(2πc/a), which is much larger than those reported before. 6. Optimization of the dielectric material distribution at the center of a two dimensional photonic crystal waveguide to adjust the energy band structure and obtain a photonic crystal waveguide structure for slow light propagation. After optimization by geometry projection method, a flat band photonic crystal waveguide is achieved with the minimum group velocity around c/2335and very small group velocity dispersion for TM mode. By using the same method, we obtain a flat band photonic crystal waveguide which can support both TE and TM modes slow light propagation, and the two polarizations have the same slow light frequency region.7. Optimization of a photonic crystal slab cavity for ultrasmall modal volume and high Q factor. We investigate the photonic crystal slab cavities with different symmetries, and try to find out the rules of increasing Q factor and reducing effective modal volume value. After optimization, we obtain a new slab cavity structure with high Q value of5.15×10and small effective modal volume value of0.09(λ0/n)3. Above two times increase for Q factor and two times decrease for the effective modal volume value is achieved by geometry projection method optimization.