Optical Properties Of Low-dimension Semiconductor Driven By A Terahertz Field

Recently, carrier coherent dynamics in low dimension semiconductor driven by a theraherz (THz) field has attracted considerable interest. When a low dimension semiconductor is driven by a THz field, there are many interesting phenomena. In this thesis, the interband and intersubband transition (ISBT) optical absorption spectra in a quantum well (QW) are numerically simulated by using density matrix theory, the optical absorption and intraband dynamics of a superlattice (SL) are investigated by using exciton basis method. The results are important for study of carrier coherent dynamics and the design of potential THz devices. The main contents and conclusions are as follows:1. The interband spectra in a QW driven by a THz field are investigated within the theory of density matrix. When a QW is driven by a THz field, splitting is shown up in excitonic peaks and replicas are formed around this peak. The intensity and position of the replicas can be controlled by changing the intensity and/or frequency of the THz field. These replicas are correspond to the sidebands in experimental spectra. With increasing the QW width, excitonic peaks shift to low-energy. In addition, the high carrier density can suppress the excitonic peaks.2.The intersubband motion equations for a QW driven by a optical field are derived. The dependence of the ISBT on QW width and many-body effects, such as Fermi-edge singularity (FES) and intersubband plasmon (ISP), is studied by using the intersubband motion equations. The ISBT optical spectra of a QW is determined by ISP and FES and the FES become dominant with decreasing the QW width.3. The optical absorption spectra and intraband dynamics in a SL under the dc and THz fields are studied by using exciton basis method. In the presence of dc and THz fields, the satellite structures in the spectra show up which are the results from the THz nonlinear dynamics of excitons. The THz field maintain the strength of the excitonic Bloch oscillations. Therefore, the oscillating time of intraband polarization is much longer than the intraband dephasing time.