Microscopic mobilities and cooling dynamics of photoexcited carriers in polycrystalline CuInSe2

Abstract

The relaxation and transport dynamics of photoexcited carriers in $p$-type stoichiometric polycrystalline CuInSe${}_{2}$ is investigated by optical-pump terahertz-probe spectroscopy. For all time delays and temperatures studied, the optically measured photoconductivity exhibits a characteristic free carrier Drude response, which allows analyzing the carrier scattering and relaxation phenomena in detail. The hot carrier distribution initially present after photoexcitation is found to relax within the first 200 ps by electron-phonon interaction with polar longitudinal optical (LO) phonons. The relaxed carrier distribution found after 200 ps indicates room temperature minority carrier mobilities close to 1000 cm${}^{2}$/Vs, in excellent agreement with Hall effect carrier mobilities previously determined for $n$-type single crystals. Analysis of the temperature dependence shows that the mobility at low temperatures is limited by ionized impurity scattering, while at room temperature the scattering of electrons with polar LO phonons dominates.