Photoexcited-carrier-induced refractive index change in small bandgap semiconductors

Using accurate band structures of InAs, InSb, and two Hg1−xCdxTe alloys, we calculate the change in refractive index caused by the photoexcited electrons and holes. The effects of both free-carrier absorption (FCA) and one-photon absorption are considered. We find that the change in refractive index varies nonlinearly with the density of photoexcited carriers and that the generally neglected FCA contribution is significant in InAs, owing to its weak spin-orbit coupling.