High photoresponsivity MoS₂ phototransistor through enhanced hole trapping HfO₂ gate 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 HfO2 gate dielectric with proper thermal annealing to demonstrate a high photoresponsivity MoS2 phototransistor. When HfO2 is annealed in H-2 atmosphere, the photoresponsivity is enhanced by an order of magnitude as compared with that of a phototransistor using HfO2 without annealing or annealed in Ar atmosphere. The enhancement is attributed to the hole trapping states introduced at HfO2 interface through H-2 annealing process, which greatly enhances photogating effect. The phototransistor exhibits a very large photoresponsivity of 1.1 x 10(7) A W-1 and photogain of 3.3 x 10(7) under low light illumination intensity. This study provides a processing technique to fabricate highly sensitive phototransistor for low optical power detection.