An Ultrafast WSe₂ Photodiode Based On A Lateral P-i-n Homojunction

In the past decade,continuous efforts have been devoted to developing high-performance optoelectronic devices based on transition metal dichalcogenides（TMDCs）.The previous researches show that high response,high sensitivity and fast response are the primary factors for manufacturing of high-performance optoelectronic devices.At present,high response and high sensitivity have been achieved,but according to previous reports,the response time of TMDCs based photodetectors lies in the time range from 10^-2 ms to 10⁵ ms.Hence,improving response speed is significant interesting for future applications of TMDCs based photodetectors.Such rather slow response times are determined by several photocarrier dynamic processes including trapping,recombination,drift and diffusion.In order to obtain a shorter response time,the device structure and photocarrier dynamic processes need to be optimized.In this paper,a WSe₂ photodiode based on lateral p-i-n junction is produced by surface charge transfer doping at contact regions before metal deposition via self-aligning argon（Ar）and oxygen（O₂）plasma treatments.Compared with previously reported TMDCs based homogeneous p-n junctions,the use of this lateral p-i-n architecture is conductive to（i）boost carrier injection/extraction by lowering contact resistance,（ii）increase photoactive volume by extending the depletion region through adding the intrinsic layer,（iii）suppress the slow photocarrier diffusion process by avoiding photon absorption at the un-depleted regions with intentional doping,（iv）diminish the possible undesired effects of doping,such as the trapping of photocarriers.As a result,a record-breaking response time of 264 ns is firstly realized by the TMDCs based photodetector.Additionally,the rectifying ratio,ideality factor,and specific detectivity of our WSe₂ p-i-n diode are comparable with or better than that of the state-of-the-art TMDCs based homogeneous p-n diodes,demonstrating a significant advantage of this work.Therefore,these excellent performances promise great prospects of our WSe₂ p-i-n photodiode in self-powered high-frequency weak signal light detection applications.Finally,we believe this study reveals a promising route to create p-i-n junction diode and ambipolar transistor for the other TMDCs,by achieving surface charge transfer doping via easy-implemented plasma treatment technique.