Dislocation Filtering Mechanism And Structral Properties Of Nano Semiconductor Materials

Nano semiconductor materials, have showed great application potential in field of modern information technology especially nanometer optoelectronics and attracted tremendous attentions due to their special electronic and optical properties. The research works presented in this doctoral thesis focus on the dislocation filtering mechanisms and structural properties of the semiconductor nano materials, especially of quantum dots. The main research work are listed below:1. Taking elastic anisotropy into consideration, we use a dislocation-position dependent model to calculate the preferential formation site of the interfacial and non-interfacial pure edge and60°mixed dislocation segment in different shaped InAs/GaAs quantum dots (QDs). From the result, it is clear that for the pure edge dislocations the most energy favorable position is always the base center of the quantum dots. While as to the60°mixed dislocations, the positions near to the edge of the quantum dot base are the energy favorable area and the exact position is changed with different aspect ratio of the quantum dot.2. A thermodynamic equilibrium approach is used to simulate the stress field and calculate the total strain energy of InAs/GaAs quantum dots in the framework of anisotropic elasticity, before and after the onset of dislocation. The model can directly calculate the strain energy in the incoherent system with the dislocation forms at any position. Taking the influence of dislocation positions into consideration and based on the energy balance between the coherent and dislocated states, the equilibrium critical size of InAs quantum dots is determined.3. An equilibrium approach is used to calculate the strain energy of InGaAs/GaAs quantum dots (QDs) before and after the onset of bending of threading dislocation (TD) into interfacial misfit dislocation (MD). The energy balance method is adopted to predict critical conditions for TD bending. We find that the critical bending area in which the inclination of TD is energetically favorable depends strongly on the QD component. The results provide guidelines for the design of quantum dot dislocation filter.4. Finite element method is used to calculate the free energy and composition distribution of InGaN/GaN quantum dot located on the InGaN/GaN pyramid. The energy balance method is adopted to predict critical conditions for quantum dot formation. We find that the formation of QD depends strongly on the size of pyramid top surface. The results can fit the experiment result qualitatively.