To date, transition metal dichalcogenides (TMDCs) are mostly explored as 2D semiconducting materials due to their distinctive properties as compared to their bulk counterparts while similar research focus on post-transition metal dichalcogenides (PTMDCs) is still in infancy. Here, we demonstrate an interesting contrast between photocarrier dynamics in quasi-2D van der Waals TlGaS2, revealed through a comparative study of single-crystal and exfoliated microflake. The single crystal exhibits pronounced temperature-sensitive spectral features indicative of strong carrier-phonon coupling and delivers a maximum responsivity of 5 mA/W under 490 nm illumination. In contrast, the microflake shows faster, weakly temperature-dependent carrier relaxation and narrowband blue-UV selectivity. Remarkably, the microflake demonstrates an enhanced responsivity of 32.1 mA/W, with a negligible response to green and red light, revealing TlGaS2 single crystals as visible photodetectors with optically tunable switching, while the microflake as a low-power, blue-UV selective, temperature-robust optical-digital conversion system. Most importantly, this work provides fundamental insight into temperature-dependent carrier transport and dimensionality-driven photocarrier dynamics in quasi-2D PTMDCs.
Bhattacharya et al. (Mon,) studied this question.