Electron Kinetics In Terahertz Quantum Cascade Laser

Terahertz (THz) technology is a hot topic in recent years and valued as one of the ten science technologies influencing the future of the world. Quantum cascade laser (QCL) is one of the main devices emitting THz electromagnetic. In this thesis, using the scatting modes of electrons, phonons and photons in the 2-dimensional structure, we researched the electron kinetics in QCL, and explored the design methods of the active region and waveguide structures in THz QCL. The results is helpful to understand further the physical mechanism in QCL and design novel THz QCLs. The main contents and conclusions are as follows:1. By investigating the electron band modes in the conduction band of multiple quantum wells, considering the discontinuity of electron effective mass at the interface of the structure, We discussed the self-consistent solution of electron energies in the active region of QCL with doping under external electric field. The results demonstrated that the more accurate solutions are obtained by expending the differential part of the Shrodinger equation as - than as -. The conclusion is important to direct the design of the active region of THz QCL.2. We analysed the electron kinetics in QCLs and find that the electron-optical-phonon scattering plays a main role in the electron population inversion in QCLs. the electron-electron scattering rate is in picosecond order with small energy gap (about several THz) and a high doping density (~ 1012cm~2), which is important in THz QCLs. The electron-photon scattering rate is lower several orders than the electron-optical-phonon scattering rates. The external electric field have significant influence on electron scattering rates between the high energy levels.3. We designed respectively the waveguide of GaAs/AlGaAs QCLs operating at 17 um by a traditional low refractive index waveguide, a single-sided metal waveguide, a double-sided metal waveguide, a waveguide with metal and high doping layer. The double-sided metal waveguide, showing the highest confinement of the optical mode intensity profile with the lowest layer thickness, is promising to be a viable waveguide solution to the QCLs in the THz range.