High Photoresponsivity and Short Photoresponse Times in Few-Layered WSe2 Transistors

Here, we report the photoconducting response of field-effect transistors based on three atomic layers of chemical vapor transport grown WSe2 crystals mechanically exfoliated onto SiO2. We find that trilayered WSe2 field-effect transistors, built with the simplest possible architecture, can display high hole mobilities ranging from 350 cm(2)/(V s) at room temperature (saturating at a value of similar to 500 cm(2)/(V s) below 50 K) displaying a strong photocurrent response, which leads to exceptionally high photoresponsivities up to 7 A/W under white light illumination of the entire channel for power densities p < 10(2) W/m(2). Under a fixed wavelength of lambda = 532 nm and a laser spot size smaller than the conducting channel area, we extract photoresponsitivities approaching 100 mA/W with concomitantly high external quantum efficiencies up to similar to 40% at room temperature. These values surpass values recently reported from more complex architectures, such as graphene and transition metal dichalcogenides based heterostructures. Also, trilayered WSe2 phototransistors display photoresponse times on the order of 10 mu s. Our results indicate that the addition of a few atomic layers considerably decreases the photoresponse times, probably by minimizing the interaction with the substrates, while maintaining a very high photoresponsivity.