Tuning Physical Properties Of Semiconductor Self-assembled Quantum Dots

Deterministic entangled photon sources is fundamentally important in quantum information science. Traditionally, entangled photons are generated via the parameter-down-convention process in nonlinear optical media. However, this method is proba-bilistic, that it has small probability to generate the unwanted multiply entangled photon pairs. It has been proposed that deterministic entangled photon pairs can be generated via biexcition cascade process in self-assembled quantum dots. However, the finite fine structure splitting, which is much larger than the natural broadening of the emission line,is the major obstruction to this proposal. This thesis is devoted to tune the fine structure splitting of exciton by external stresses.The major results in this work are listed below.1. Finite temperature empirical pseudopotential theory: To study the tem-perature dependent optical properties of quantum dots, we developed a temperature-dependent empirical pseudopotential theory. The temperature may dramatically affect the optical properties of quantum dots, such as the red shift of emission lines. In our ap-proach, the temperature dependence is introduced by the temperature-dependent Debye-Waller factor. We determine the corresponding parameters by fitting the effective mass,energy gap as well as the temperature dependent emission energies at the high symmet-ric points of bulk materials. We calculate the temperature dependent exciton energies in quantum dots, which agree with the experimental data very well. We find that the fine structure splitting of exciton will not be dramatically affected by the temperature effect.2. Tuning of fine structure splitting of exciton by external stress: We show that the fine structure splitting of exciton can be efficiently tuned by external stresses.We discuss the role of uniaxial stress and biaxial stress on the fine structure splitting of quantum dots. We show that the fine structure splitting can be tuned to nearly zero for general quantum dots via two independent stresses, which has been verified experimen-tally.3. Theoretical model for fine structure splitting in quantum dots: By using Bir-Pikus model, we derived the theoretical model that describe how the fine structure splitting change under external stresses, which allow us to understand the microscopic mechanism of how the stresses change the fine structure spitting and exciton polariza-tion angles.4. An wavelength tunable entangled photon source: The quantum dots entan-gled photon emissions have been demonstrated experimentally. However due to the structure difference in quantum dots, the emission wave lengths in quantum dots are generally different from dot to dot, and therefore the entanglement between photons from two quantum dots are impossible to be realized. We demonstrate that with three independent external stressed we can eliminate the fine structure splittings and tune the wave lengths simultaneously. This provides a first step to the future realization of scalable entangled photon-pair generators for quantum information applications.