Semiconductor Intersubband Dynamics And Terahertz Oscillator

Terahertz (THz) field can strongly modify the quantum states of Low-dimension (LD) semiconductor and influence their electronic and optical properties. Meanwhile, the intersubband dynamics in LD semiconductor are the theoretical foundation of semiconductor THz sources and the correlative optoelectronic devices. In this thesis, we have investigated the transport and optical properties in LD semiconductor driven by THz radiation, and explored the THz oscillator based on superlattice and resonant tunneling structure (RTS). The main contents and conclusions are as following:1. THz switch based on the double barrier RTS is studied. Using the Wigner-Poisson transport model, we have calculated the I-V curve and transient current density of RTS, and studied its dynamical instability in the presence of the THz field. It's found that the THz field may trigger the switching between different current states in a few picoseconds, suggesting that the system may potentially act as the THz switch and THz detector.2. Tunable THz Bloch oscillations (BO) in the superlattice and THz current oscillations in RTS are investigated. By using the transfer matrix method and the scattering state approach, we have studied the optical properties of the superlattices with thickness gradual variation or large thickness microcavity. The optical BO and Wannier-Stark ladders are obtained in both superlattices. The frequency of BO is in THz range and can be modified by changing the grads of thickness or size of microcavity. In terms of the energy-level model, the time-dependent potential and electron density are calculated. So the current density of RTS behaves the THz oscillation.3. The Bloch equations for semiconductor intersubband driven by a optical field are derived. The influence of intersubband resonance (ISBR) of quantum wells on the Coulomb interaction, electron density and lattice temperature is discussed. The line shape and peak position are determined by the interplay of different collective excitations. The increase of lattice temperature can red-shift and reduce the absorption. The nonparabolicity of sub-band can restrain the intersubband plasmon. The THz-induced sideband and Autler-Towns splitting in the absorption spectrum are obtained...