| 研究実績の概要 |
A Non-Equilibrium Green’s Function (NEGF) method has been used to analyse the carrier transport and gain properties of GaN/AlGaN THz QCL structures. A considerable advantage of the NEGF formalism is the built-in description of the time-energy uncertainty principle linking the calculation of the scattering processes and the level broadening. In addition, the gain is calculated in a self-consistent way accounting for the correlation effects in the broadening of different levels. The simulation results demonstrate that (i) the main contribution to the broadening of laser levels in GaN THz QCL does not come from LO-phonon scattering but comes from other mechanisms, namely electron-electron (e-e) scattering and charged impurity scattering (CIS); (ii) the gain spectra can be narrow enough and the peak gain can be high enough for lasing at 7 THz at 280 K for a preliminary design.These are published on APL, "Broadening mechanisms and self-consistent gain calculations for GaN quantum cascade laser structures".
The GaN THz QCL waveguides are carefully investigated. The possible methods have been developed to fabricate low loss and high confinement waveguide for both single-metal-surface-plasmon and double-metal designs. The results are published on JJAP,"Controlling loss of waveguides for potential GaN terahertz quantum cascade lasers by tuning the plasma frequency of doped layers".
Epitaxial growth technology for GaN/AlGaN THz QCL structures have been developed by using both MBE and MOCVD methods. High quality QCL structures have been achieved.
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