Optical gain of strained GaAsSb/GaAs quantum-well lasers: A self-consistent approach

Abstract

We present a self-consistent model for the band structure and optical gain spectrum of GaAs1−xSbx/GaAs quantum-well (QW) lasers with carrier population. Experimental data indicate that this material system has a type-II QW configuration. By fitting the experimental photoluminescence data from various groups using our proposed empirical model, which assumes that 90% of the band-gap bowing parameter (1.2 eV) appears in the valence band, we find that the unstrained valence band edge discontinuity ratio Qv0 is close to 0.9 for an arbitrary Sb mole composition x of GaAs1−xSbx/GaAs QWs and the QW structure becomes type-II when the compressive strain induced band-edge shifts are taken into account. We show that for type-II QWs the self-consistent solution, which solves the Schrödinger equation and Poisson equation simultaneously, is necessary. Due to the free-carrier screening effect in the self-consistent potential, the electrons are attracted toward the barrier–well interfaces by the holes in the wells, and, therefore, sufficient gain can be achieved for lasing action with type-II QWs. Our theoretical results are compared with experimental data of laser operation wavelength and modal gain, with reasonable agreement. Our model will be important for modeling of type-II QW lasers and useful for design of GaAsSb/GaAs QW vertical-cavity surface-emitting lasers.