Numerical Simulation Of Active Region In Terahertz Quantum Cascade Laser

Terahertz (THz) source is an active research field in recent years. With radiation frequency determined by the energy space of the lasing subbands, Quantum cascade laser (QCL) has been the preferred choice of compact, low-consumption, portable THz source. In this thesis, a detailed discussion of energy subbands and interface phonon assisted transition in GaAs/AlGaAs QCL is presented. The calculation can be easily applied to the design and simulation of QCL. The main contents and conclusions are as follows:1. Our approach to energy subbands in the active region of QCL is k · p method. Electron eigenvalues and eigenstates are calculated by solving Schrodinger and Poisson equations self-consistently. The discontinuity of electron effective mass at the interface of the structure is considered during the calculation. The anti crossing point of external electric field is presented. The accurate calculation of subbands build solid foundation for the later discussion of interface phonon assisted scattering in THz QCL.2. The confined phonon modes and interface phonon modes are discussed based on macroscopic dielectric continuum model (DMC). Interface phonon modes dispersion relationship is calculated by transfer matrix methods (TMM). Interface phonon assisted scattering rate is obtained straightforwardly by Fermi Golden Rule, our approach here is the same as Kinsler's. The phonon-electron scattering rate is in picoseconds order. The AlAs-like and upper GaAs-like interface phonon modes contribute most of the scattering rate. Interface phonon modes couple strongly with electrons at E₂ And the magnitude of scattering rate between E₂ and E₁ is much larger than that between E₃ and E₁, which is helpful for the laser inversion between E₃ and E₂. The calculation can be easily applied to the design and simulation of QCL.