High performance WSe2 phototransistors with 2D/2D ohmic contacts.

We report high-performance WSe2 phototransistors with two-dimensional (2D) contacts formed between degenerately p-doped WSe2 and undoped WSe2 channel. A photoresponsivity of similar to 600 mA/W with a high external quantum efficiency up to 100% and a fast response time (both rise and decay times) shorter than 8 mu s have been achieved concurrently. More importantly, our WSe2 phototransistor exhibits a high specific detectivity (similar to 10(13) Jones) in vacuum, comparable or higher than commercial Si- and InGaAs-based photodetectors. Further studies have shown that the high photoresponsivity and short response time of our WSe2 phototransistor are mainly attributed to the lack of Schottky-barriers between degenerately p-doped WSe2 'source/drain contacts and undoped WSe2 channel, which can reduce the RC time constant and carrier transit time of a photodetector. Our experimental results provide an accessible strategy to achieve high-performance WSe2 phototransistor architectures by improving their electrical transport and photocurrent generation simultaneously, opening up new avenues for engineering future 2D optoelectronic devices.