Electrical and Optoelectronic Properties Analysis in Two-dimensional Multilayer WSe2 Phototransistor for High Speed Device Applications

In this work, we fabricated back gated multilayer WSe2 phototransistor with Au/Ti as electrodes whose electrical properties were investigated over a wide range of temperature T from T = 5.4 to T = 350 K from which several electrical parameters including mobility μ and barrier height ϕms were extracted to analyze their T-dependencies. For example, the T-dependent mobility μ was characterized by a peak at ~ 250 K after which point μ decreased according to μ ~ T-0.71, attributed to phonon scattering. Additionally, ϕms was found to be 29 meV at VG = 0 V which decreased as VG increased in alignment with barrier modulation theory. Finally, optoelectronic properties of our Au/Ti/WSe2 field effect transistors (FETs) were investigated by exposing the device to a tunable laser, where the photoresponsivity R was calculated to be ~ 43 A/W at an optical power of 0.786 nW. The phototransistor also showed very short response time with τrise = 10 ms, and Tfall = 3 ms. Our work demonstrates excellent potential of WSe2 as a promising 2D semiconductor for high speed electronics and opto-electronics.