Photocarrier Dynamics in TlGaS₂ Nanoflakes and van der Waals Heterostructures with Hexagonal Boron Nitride and WS₂ Nanoflakes: Implications for Optoelectronic Applications

We present an experimental investigation on photocarrier dynamics in a TlGaS2 bulk crystal and its heterostructures with hexagonal BN and WS2. The samples were obtained by mechanical exfoliation and dry transfer techniques. The photocarrier dynamics was monitored by a transient absorption technique. We observed a direct optical transition of about 555 nm in the TlGaS2 crystal. By utilizing transient absorption of that transition, we obtained a hot-carrier energy relaxation time of less than 1 ps and a carrier lifetime of about 300 ps in TlGaS2 at room temperature. In the hexagonal-BN-TlGaS2 heterostructure, the photocarrier dynamics was similar to that in TlGaS2, indicating the type-I band alignment of this structure with both band extremes located in TlGaS2. In the monolayer WS2-TlGaS2 heterostructure, we observed charge transfer from TlGaS2 to WS2 and an extended lifetime of the transferred carriers in WS2. These results introduce TlGaS2 as a promising layered material for developing two-dimensional van der Waals materials that can be combined with other two-dimensional materials for various optoelectronic devices.