Photogating-driven enhanced responsivity in a few-layered ReSe₂phototransistor

A wide variety of two-dimensional (2D) metal dichalcogenide compounds have recently attracted much research interest due to their very high photoresponsivities (R) making them excellent candidates for optoelectronic applications. HighRin 2D photoconductors is associated with trap state dynamics leading to a photogating effect, which is often manifested by a fractional power dependence (γ) of the photocurrent (I_ph) at an effective illumination intensity (P_eff). Here we present photoconductivity studies as a function of gate voltages, over a wide temperature range (20 K to 300 K) of field-effect transistors fabricated using thin layers of mechanically exfoliated Rhenium Diselenide (ReSe₂). We obtain very high responsivitiesR∼ 16500 A/W and external quantum efficiency (EQE) ∼ 3.2 × 10⁶% (at 140 K,V_g= 60 V andP_eff= 0.2 nW). A strong correlation betweenRandγwas established by investigating the dependence of these two quantities at various gate voltages and over a wide range of temperatures. Such correlations indicate the importance of trap state mediated photogating and its role in promoting high photo-responsivities in these materials. We believe such correlations can offer valuable insights for the design and development of high-performance photoactive devices using 2D materials.