Optical gain in strain-free and strained layer Ga XIn 1−XAs/InP superlattices

Abstract

We report on the experimental determination of unsaturated optical gain spectra in Ga XIn 1−XAs/InP multiple quantum well heterostructures (MQWHs). For the first time a pronounced step-like lineshape of the optical gain spectra is observed, directly reflecting the two dimensional (2D) nature of the carrier system. The optical gain (lineshape and peak gain values) in QWHs is completely different for TE and TM polarization in contrast to bulk material where it is isotropic. An excellent description of all experimental data is obtained by applying a microscopic theory for the radiative recombination processes. Two-dimensional carrier densities are derived from detailed lineshape fits and range up to 9.6·10 12 cm −2 at room temperature. In In-rich QWHs (x<0.47) the gain is suppressed for TM polarization as compared to GaInAs layers lattice-matched to InP. The enlarged anisotropy of the optical gain is explained by higher separations between light and heavy hole subbands which result from the biaxial compression of the GaInAs wells.