Guiguang Xiong

Quadratic electro-optic effects and electro-absorption process in InGaN/GaN cylinder quantum dots

Abstract We carried a detailed calculation of quadratic electro-optic effects (QEOE) and electro-absorption (EA) process as a function of pump photon energy ħω in InGaN/GaN cylinder quantum dots. The third-order susceptibility dispersion behaviors of direct current are obtained. It is found that with the increase of the quantum dot (QD) height and radius, the magnitudes of the real part of the quadratic electro-optic susceptibility and the imaginary part of the EA susceptibility increase at the resonant frequency, and its resonant position shifts to the lower energy region. In addition, lower In content induces larger χ (3) .

Characteristics of quadratic electro-optic effects and electro-absorption process in CdSe parabolic quantum dots

The nonlinear susceptibilities have been calculated theoretically for CdSe disk-like parabolic quantum dots by using a two-energy-level model in the strong-confinement regime. The confined wave functions and eigenenergies of excitons in parabolic quantum dots have been studied by solving the electron-hole effective-mass Schrodinger equation. The third-order susceptibilities of the quantum dots for quadratic electro-optic effects (QEOE) and electro-absorption (EA) process as a function of quantum dot size, relaxation time, parabolic confinement frequency, and pump photon energy have been also analyzed.

Exciton enhancement effect on the third harmonic generation in ZnS/CdSe quantum dot quantum well

Exciton enhancement effect on the third-order optical nonlinearities of a ZnS/CdSe quantum dot quantum well (QDQW) has been theoretically studied. The wave functions and eigenenergies of excitons in QDQW have been calculated under the effective-mass approximation. By solving a three-dimensional nonlinear Schrodinger equation and by means of compact density matrix method, the third-order nonlinear susceptibilities for third-harmonic generation (THG) have been calculated in a two energy levels model of QDQW. Firstly, we studied the size effect on THG in QDQW. Then we compared the value of THG with the case that only considering electron states. The results show that the THG is greatly enhanced when compared with the condition just considering electron states.

Quantum-confined Stark shift in electroreflectance of a cylindrical GaN quantum dot

Abstract The electroreflectance (ER) spectra in the presence of the modulated electric field have been employed to study the fine structure of a cylindrical GaN quantum dot (QD), including the light hole and heavy hole interband transitions, and the ER spectra exhibit Franz–Keldysh oscillation characteristics with abscissa of energy ( E − E g ). The quantum-confined Stark shift (QCSS) happened when the electric field intensity increased and the light and heavy holes dependent characteristics have been shown. The three-dimensional Schrodinger equation of QD has been calculated within the framework of effective-mass approximation, and the ER indices have been obtained from modulation absorption coefficients using the Seraphin coefficients and the Kramer–Kroning relation.

Spin-orbit splitting-dependent quadratic electro-optic effect in InGaN/GaN quantum wells

Taking account of the contribution of spin–orbit splitting, the energy band of GaN/InGaN quantum wells (QWs) has been calculated. For the quadratic electro-optic effect (QEOE), the resonant third-order nonlinear optical susceptibility due to the interband transition of the mode, whose polarization is parallel to the [0 0 1] direction of the QWs, has been analysed as a function of the well width and the concentration of In.

Polaron Effects on the Third-Order Susceptibility of a CdSe/ZnS Quantum Dot Quantum Well

Theoretical investigation of the polaron effects on the third-order susceptibility associated with the intersubband transition in the conduction band in a CdSe/ZnS quantum dot quantum well is presented. Contributions from the confined longitudinal optical (LO) and surface optical phonon modes are considered and the wave function is derived under the frame work of the perturbation theory. We carried a detailed calculation of third-harmonic generation (THG), Quadratic electro-optic effects (QEOE), and electro-absorption (EA) process on such a quantum dot as a function of pump photon energy with different incident photon energy and under different sizes. The results reveal that the polaron effects are quite important especially around the peak value of the third-order susceptibility. By increasing the size of the quantum dots, the peaks of χ(3)THG, χ(3)QEOE, and χ(3)EA will shift to the lower energy, and the intensities of the peaks will increase.

Spin-orbit splitting dependent resonant third-order nonlinear optical susceptibility in InGaN/GaN multiple quantum wells

For the transition between valence band and conduction band, the third-order nonlinear optical susceptibility χ(3) for degenerated four-wave mixing in InxGa1-xN/GaN multiple quantum wells (MQWs) has been calculated. The contributions of spin-orbit split-off energy to the resonant third-order nonlinear optical susceptibility of the modes, whose polarization is vertical to the [001] direction of the MQWs, are discussed in detail. The correlations between the peaks of χ(3), which are due to the transitions from the spin-orbit split-off energy level to first conduction subband, and the width of the quantum well and the constituents of the semiconductor material are obtained.