Optical Properties Of Low-dimensional Quantum Structures In THz Range

Many characteristic energies of low-dimensional semiconductor structures lie in the terahertz (THz) range. Therefore there is a strong interaction between electrons and the THz field in low-dimensional semiconductor structures. The study on the optical absorption in THz regime in low dimensional semiconductors is an importance topic in the research field of terahertz optoelectronics. By employing density matrix method and perturbation theory, the intra- and inter-band absorption properties have been investigated qualitatively and quantitatively. The main conclusions are as follows:1 .By taking in account the interaction of electrons with different phonon modes, the optical absorption coefficient of quantum wells under a static magnetic field in the THz regime has been calculated within the perturbation theory. The dependence of the optical absorption on the quantum well width and the electron temperature has been studied. The results indicate that the interaction of electrons with the bulk-, confined- and interface-phonon modes play an important role on the absorption while the effect due to the electron-half-space-phonon scattering is relatively weak. It is found that the absorptions due to different phonon modes depend on the well width and electron temperature quite differently. The total absorption increases with the well width and the electron temperature.2. The plasma absorption spectra of the parabolic quantum well under an electric field and a magnetic field in Voigt configuration is studied. By using a unitary transformation, the plasmon excitation spectra in a quantum well under an intense THz field has been calculated. It is found that the excitation spectra are discrete due the multi-photon processes and inter-Landau level transitions. The quantum well confining potential decreases as the magnetic field increases. This has led to the changeover to a 3 dimensional system and the increase of the plasmon energy.3. The exciton absorption spectrum in double quantum well is investigated by using the theory of density matrix. The results indicate that the satellite peaks show up due to the interaction between the exciton and THz field. There exist charged exciton due to the coupling between excitons with free carriers, which induce the increasing of the satellite peaks.