Terahertz Quantum Cascade Lasers And Other Semiconductor Sources

Terahertz (THz) technology has been the focus of intense research in recent years and is identified as one of the ten emerging technologies that will change our world. The realization of compact solid-state THz sources is the key problem in THz technology. THz wave lies between the microwave and the infrared regime, so THz radiation can be generated by using either electronics or phonics. In this thesis, we study the hot electron and phonon transport in resonant phonon assisted THz quantum cascade lasers (QCLs). It is found that the nonequilibrium hot phonons are important in the determination of the device current. We also study the possibility of generating THz oscillations using the negative differential conductivity (NDC) in the electronic system. The main results are as follows:1. We have developed the THz QCL simulation program based on the Monte Carlo method, and have studied the hot electron and phonon transport in resonant-phonon-assisted THz QCLs. It is found that the hot phonon effect and the electron-impurity scattering are important for the determination of electron subband occupation and device current of the QCL. We found that nonequilibrium LO phonons may modify the electron-phonon interaction, and consequently change the device current. It is shown that the electron-impurity scattering supplies an additional channel for the electrons to be injected into the next period of the QCL. It is as important as the electron-electron interaction. Therefore, in the absence of the hot phonon effect and/or the electron-impurity scattering, we will under-estimate the current of resonant-phonon-assisted THz QCLs. This Monte Carlo program is the theoretical tool for the design and optimization of THz QCLs.2. Based on the band structure of zinc-blende GaN from ab-initio calculation, we proposed a THz oscillator utilizing the negative differential conductivity due to the inflection point in its Γ valley. We found that this n~+nn~+ oscillator has a self-oscillating frequency in the THz range. We have carefully studied the electric domain dynamics and the self-oscillation frequency dependence on the applied dc field. Moreover, when the diode is driven by a dc and an ac biases, a typical nonlinear dynamic system has been constructed with the dc...