Terahertz relaxation dynamics of a two-dimensional InSe multilayer

Optical pump-terahertz probe measurements are performed to study the photoexcited carrier dynamics of the In-rich two-dimensional InSe multilayer, which is a promising candidate for future high performance electronic and photoelectronic applications. According to the transient terahertz measurements, the intraband and interband relaxation processes can be clearly identified from different carrier relaxation lifetimes. The intraband relaxation consists of an ultrafast (∼2 ps) carrier-optical phonon scattering and relatively slower (∼10 ps) anharmonic scattering of hot optical phonon. The subsequent interband recombination is dominated by a Shockley-Read-Hall recombination with lifetime on order of 100 ps. Because the grown polytype In-rich InSe multilayer has a high defect density, the primary recombination channel is through the defects in the surface, but the bulk recombination increases rapidly with temperature and can catch up the contribution of the surface recombination at high temperature.