High photoresponsivity MoS₂phototransistor through enhanced hole trapping HfO₂gate dielectric

Phototransistor using 2D semiconductor as the channel material has shown promising potential for high sensitivity photo detection. The high photoresponsivity is often attributed to the photogating effect, where photo excited holes are trapped at the gate dielectric interface that provides additional gate electric field to enhance channel charge carrier density. Gate dielectric material and its deposition processing conditions can have great effect on the interface states. Here, we use HfO₂gate dielectric with proper thermal annealing to demonstrate a high photoresponsivity MoS₂phototransistor. When HfO₂is annealed in H₂atmosphere, the photoresponsivity is enhanced by an order of magnitude as compared with that of a phototransistor using HfO₂without annealing or annealed in Ar atmosphere. The enhancement is attributed to the hole trapping states introduced at HfO₂interface through H₂annealing process, which greatly enhances photogating effect. The phototransistor exhibits a very large photoresponsivity of 1.1 × 10⁷A W^-1and photogain of 3.3 × 10⁷under low light illumination intensity. This study provides a processing technique to fabricate highly sensitive phototransistor for low optical power detection.