Phonon lifetime in SiSn and its suitability for hot-carrier solar cells

We present a phononic and electronic study of SiSn in the zinc-blende phase. A detailed description of the longitudinal optical (LO) phonon decay in a three-phonon process is presented together with the corresponding lifetime. The necessity to go beyond the zone center phonon approximation in this case is highlighted as it reveals a steep dependence of the lifetime on the initial phonon wavenumber, which differs from usual semiconductors. The electronic band structure is calculated within the GW formalism and shows a small direct band gap. It is shown that the LO-phonon resulting from electron cooling has a lifetime four to eight orders of magnitude above all the known value in semiconductors for this process. We finally show the suitability of SiSn for hot-carrier solar cells, as it is endowed with ultra-slow cooling of hot carriers.