Ultrafast and ultrasensitive phototransistors based on few-layered HfSe2

Two-dimensional layered materials have exhibited great potential in electronic and optoelectronic applications, because of their unique chemical and physical properties. Recently, Hf-based transition metal dichalcogenides are predicted to own high room temperature mobility and are attracting increasing interest. However, only few experimental investigations are reported hitherto. In this paper, we demonstrate ultrafast and ultrasensitive back-gated HfSe2 phototransistors. Au-contacted HfSe2 phototransistors display a high on/off ratio of 106 and modest mobilities in the range of 2.6-6.5 cm2 V-1 s-1. Additionally, the phototransistors based on HfSe2 present prominent optoelectronic performance with a high responsivity of 252 A/W and an ultrafast response time of 7.8 ms, implying the sensitive photoswitching behavior. Moreover, the response time can be modulated by gate voltages. The excellent field effect transistor performance coupled to the sensitive and fast photodetection makes HfSe2 have a broad application prospect for electronic and optoelectronic devices in the future.