Studies Of Third-order Nonlinear Optical Susceptibility In InGaN/GaN Quantum Dot

The resonant third-order susceptibilities at various directions in self-assembled InGaN/GaN cylinder quantum dots and the size distribution of dots, which affects the susceptibilities dramatically have been both investigated. Due to stronger build-in electric field, the piezoelectricity has been taken into account in this thesis.At first, quantum effects, the fabrication methods of semi-conductor quantum dots and theory of energy bands of quantum dots have been introduced briefly.Secondly, three kinds of methods to calculate the third-order susceptibility, including classic theory, semi-classic theory and quantum theory have been presented. In this part, we focus on the third method: utilizing density matrix to obtain the formula of the third-order susceptibility.Then, the confined wave functions and energies of electrons in the dots have been calculated in the effective-mass approximation by solving the 3D Schrodinger equation, in which a strong build-in electric field effect due to the piezoelectricity and spontaneous polarization have been taken into account. We discover that build-in electric field, wave function and energy of electrons are all different with the different content of In in InGaN/GaN quantum dots. Furthermore, we calculated resonant third-order susceptibilities at various directions and explored the effect of size distribution of quantum dots on the susceptibilities. At last, the nonlinear absorption/gain has been discussed at the presence of exciton and biexciton.