Ultimate Limit in Optoelectronic Performances of Monolayer WSe2 Sloping-Channel Transistors

Atomically thin monolayer two-dimensional (2D) semiconductorswithnatural immunity to short channel effects are promising candidatesfor sub-10 nm very large-scale integration technologies. Herein, theultimate limit in optoelectronic performances of monolayer WSe2 field-effect transistors (FETs) is examined by constructinga sloping channel down to 6 nm. Using a simple scaling method compatiblewith current micro/nanofabrication technologies, we achieve a recordhigh saturation current up to 1.3 mA/& mu;m at room temperature,surpassing any reported monolayer 2D semiconductor transistors. Meanwhile,quasi-ballistic transport in WSe2 FETs is first demonstrated;the extracted high saturation velocity of 4.2 x 10(6) cm/s makes it suitable for extremely sensitive photodetectors. Furthermore,the photoresponse speed can be improved by reducing channel lengthdue to an electric field-assisted detrapping process of photogeneratedcarriers in localized states. As a result, the sloping-channel deviceexhibits a faster response, higher detectivity, and additional polarizationresolution ability compared to planar micrometer-scale devices.