Unconventional Thermally Activated Indirect to Direct Radiative Recombination of Electrons and Holes in Tin Disulfide Two-Dimensional van der Waals Material

Tin disulfide (SnS2) is a two-dimensional semiconducting van der Waals material with an indirect band gap. We measured the mobility and recombination dynamics of charge carriers as a function of temperature and charge density. Excess electrons and holes were generated by pulsed irradiation with 3 MeV electrons. The charge carriers were probed by time-resolved microwave conductivity measurements. The mobility and decay pathways of the charge carriers were determined by a global kinetic rate equation model including decay of charges by recombination and trapping. We found high mobilities for electrons and holes near 100 cm(2) V-1 s(-1). The mobility decreases at higher temperature, which is typical for bandlike transport. The second-order recombination rate constant is found to be thermally activated with an activation energy close to the energy difference of the direct and indirect band gap of SnS2. We demonstrate that the radiative recombination is reaction-limited and takes place via the Gamma-point after thermal excitation of electrons from the M-point to the Gamma-point, while a phonon emission-related recombination between the indirect band gap (M-point electrons and Gamma-point holes) has no relevant contribution to the population decay. The observed effects result in an unusual increase of radiative electron-hole recombination constant with temperature.