The Theory Study Of Gan-based Quantum Cascade Lasers

At the present, the quantum-cascade laser (QCL) has extended the emissionwavelength from mid-infrared to terahertz (THz) spectral range, it is ideal terahertzoscillating source. It is applied in many areas and value for socioeconomic. In this thesis,the design of AlGaN/GaN quantum-cascade lasers (QCLs) has been investigateddetailedly, the distributions of conduction subband structure and the electron wavefunction have been gained by calculating one-dimensional Schrodinger equation. The Alcomposition, the external bias, energy difference of conduction subband and productionaberration had been studied, and their effects on properties of lasers had been analysed.The result was value for improving the properties of lasers.1.The distributions of conduction subband structure and the electron wavefunction of were solved with the transfer matrix method through Matlab calculatingone-dimensional Schrodinger equation. The specific polarization effect of GaN havebeen analysed, which causes opposite polarization field in well and barrier layers.2.The three-level and four-level AlGaN/GaN QCLs realize population inversionby means of longitudinal optical phonon scattering, cascade by tunneling and meet thenear-resonant conditions strictly, stimulated radiation is created finally.3.The structure and the Al composition were fixed, the effects of the external biason lasers were analysed, the results showed that the external bias must be proper toobtain the largest dipole matrix element. Similarly, the width of layers and the externalbias were invariant, optimal Al composition was selected to meet the near-resonantconditions and realize population inversion. The smaller Al composition can not meetthe near-resonant conditions, larger Al composition will impact growth aberration andreduce the rate of transition. When the structure was changed, the conditions realizingstimulated radiation was also varied to gain THz wave, the lasing frequency weredifferent finally.