Effects of band nonparabolicity on the gain and current density in EuSe-PbSe0.78Te0.22-EuSe IV-VI semiconductor quantum-well lasers

In this work, a theoretical model that calculates the gain versus current density relationship for IV-VI semiconductor quantum-well lasers was developed. The model, based on Kane's two-band model, solves for the anisotropy in the constant energy surfaces and for the strong nonparabolicity of the bands. The system investigated was the EuSe-PbSe0.78Te0.22 quantum-well structure at 77 K. The nonparabolicity of the bands in the growth direction was found to shift the energy levels in the PbSe0.78Te0.22 quantum well to lower energies as compared to a quantum well with parabolic bands. Nonparabolicity of the bands also resulted in an energy dependent density of states in the junction plane of the structure. The effect of nonparabolicity in all directions on the gain versus current density relation is a reduction in the current density needed for any given gain and an increase in the gain saturation level. In addition to the 20% shift in the output lasing energy, nonparabolicity of the bands lowers the values of the confinement factor relative to those for the parabolic bands which in turn lowers the modal gain values.