Modeling of optical gain in InGaN-AlGaN and In/sub x/Ga/sub 1-x/N-In/sub y/Ga/sub 1-y/N quantum-well lasers

This paper presents computations of the optical gain in In/sub x/Ga/sub 1-x/N-In/sub y/Ga/sub 1-y/N and InGaN-AlGaN quantum-well lasers involving the contributions of excitons as well as free carriers transitions. The behavior of optical gain in GaN based quantum wells due to excitonic transitions is quite similar to that of ZnCdSe-ZnSSe system, as the magnitude of the exciton binding energies (/spl sim/30 meV) is comparable. The model compares the exciton emission energy with the experimental data reported on In/sub 0.22/Ga/sub 0.78/N-In/sub 0.06/Ga/sub 0.94/N multiple quantum wells as well as in GaN layers (cubic grown on 3C SiC), including the effect of strain induced band gap changes. The optical gain is also computed as a function of the injection current density for the InGaN-AlGaN multiple quantum-well lasers. The model evaluates the feasibility of obtaining GaN based blue and ultraviolet lasers. It is shown that the excitonic transitions reduce the threshold current density which is adversely affected by the presence of dislocations and other defects.