Exciton-Like and Mid-Gap Absorption Dynamics of PtS in Resonant and Transparent Regions

Two essential ranges of energy within and out of bandgap determine the global optical property of a general semiconductor. Here, exciton-like inter-sub-band resonance absorption and optical bleaching of platinum sulfide (PtS) in the resonant region are found and investigated through the linear optical spectra and ultrafast transient absorption spectra. Besides, free-carrier absorption and defect-assisted Auger recombination in the transparent region are identified via the intensity- and temperature-dependent pump–probe experiments. Good experimental and theorical agreements are obtained using the mid-gap carrier-capture model considering the complex optical conductivity based on the rate equations. This work facilitates further understanding of the ultrafast photoinduced carrier behavior in PtS, which provides the possibility for future applications in photoelectric devices.