Abstract

The absorption and gain of electromagnetic radiation by electronic transitions over the fundamental gap as a function of carrier density, wavelength, polarization of radiation and strain has been well characterized. In contrast, the influence of these parameters on the absorption by intervalence band transitions (IVBA) has been investigated less thoroughly. Such transitions occur at higher values of the crystal momentum, where the interaction of the valence bands with the conduction band is non-negligible. Consequently, at least an 8-band k-p model is required including the lowest conduction (C), heavy hole (HH), light hole (LH), split-off (SO) band, and spin, to allow optical matrix elements to be consistently calculated according to actual symmetries of wave functions [1]. IVBA is often neglected in laser models, though there is both experimental and theoretical evidence of its significance [2]. In this contribution we present a theoretical calculation of both IVBA and gain, in order to elucidate their relationship, the role of the different bands involved and the magnitude of strain-induced optical anisotropies. We demonstrate that IVBA has a strong influence on the laser threshold of such materials.

© 1996 Optical Society of America