Optical And Transport Properties Of Semiconductor Quantum Dot Structures

In this dissertation, we mainly focus on a theoretical study of the optical prop-erties of semiconductor quantum dot structures, including optical absorption prop-erties, quantum interference effects and nonlinear optical effects induced by intense fields. In particular, we use the transport properties of the quantum dot structures to obtain the optical signals induced by weak fields.In the first part of the dissertation, the response of coupled quantum dots and quantum rings to weak optical fields are investigated.Firstly, we systematically study the interference phenomena of serially coupled triple quantum dots driven by a strong driving and a weak probe field. The probe absorption spectra are shown in the photon-assisted tunneling current, which pro-vides a feasible way to obtain weak coherent optical signals in a solid environment. By changing the configuration of the three-level coupled triple quantum dot, we can obtain and control various quantum coherent properties such as Autler-Townes splitting, Mollow triplet, gain effect without population inversion, and coherent pop-ulation trapping. We also find that the effect of spontaneous emission of phonons may lead to an obvious background current, which can be used to distinguish which transition is driven by the driving field in experiments.And then we investigate the magnetic-field-modulated terahertz absorption spectra of a real GaAs quantum ring. As the energy levels of the quantum ring are modulated by an external magnetic field, the photon-participated tunneling current is used to show the features of the terahertz spectra of the quantum ring. Our study provides a possible way to realize tunable detection of terahertz fields. In such a scheme, tuning is performed via the external magnetic field, and the resonant frequency bands are handled by controlling the radius and width of the quantum ring.In the second part of the dissertation, the features of high-order harmonic generation in quantum dots and coupled quantum dots are explored.We first study the high-order harmonic spectra of a quantum dots driven by an intense microwave field. We propose a way to obtain terahertz radiation by using these nonlinear optical effects. By mapping the optical processes to quantum transport processes, we find that the efficiency of high-order harmonic generation is determined by the bandwidth of the quasienergy spectrum.Finally, we explore the features of high-order harmonic generation in coupled triple quantum dots in intense microwave fields. We find that multi-level systems in coupled triple quantum dots can generate odd-even order harmonics. The dynamic mechanism of high-order harmonic generation in optical coupled multi-level system is investigated. In addition, we make an elementary study on the polarization of the radiation. Due to the spatial configuration of the coupled triple quantum dots, the harmonic emission can be either linearly or elliptically polarized when driven by linearly polarized fields, and the polarization properties are found to be strongly dependent on the harmonic order.