Optical gain of interdiffused InGaAs-GaAs and AlGaAs-GaAs quantum wells

We have analyzed theoretically the effects of interdiffsuion on the gain, differential gain, linewidth enhancement factor, and the injection current density of In _0.2Gao, _0.8As-GaAs and Al _0.3Ga _0.7As-GaAs quantum-well (QW) lasers. We have calculated the electron and hole subband structures including the effects of valence band mixing and strains. The optical gain is then caculated using the density matrix approach. Our results show that the gain spectrum can be blue-shifted without an enormous increase in the injected current density. Imposing an upper limit (416 A-·m ^-2) on the injection current density for a typical laser structure, we find that the InGaAs-GaAs and AlGaAs-GaAs QW lasers can be blue-shifted by 24 and 54 nm, respectively. Our theoretical results compare well with the tuning ranges of 53 and 66 meV found for AlGaAs-GaAs QW's in some experiments. This indicates that the interdiffusion technique is useful for the tuning of laser operation wavelength for multiwavelength applications.