Linear and two-photon absorptions of Si-Ge strained-layer superlattices

Linear and two-photon absorption spectra of Si-Si0.5Ge0.5 strained-layer superlattices grown along [001], [111], [110] directions are calculated within a realistic microscopic model. The temperature dependence of carrier lifetimes due to deformation-potential scattering (including intra- and intervalley scattering) has been taken into account. It is found that superlattices grown along the [110] direction are most promising for applications both in far-infrared detection and in optical limiting. The value for the two-photon absorption coefficient at 77 K for an incident 10.6-μm radiation polarized parallel to the layer can be as high as 150–2000 cm/MW with a linear absorption coefficient around 600–3500 cm−1.