Characterization of Few layer Tungsten diselenide based FET under Thermal Excitation

Abstract

Two-dimensional (2D) materials are very promising with respect to their integration into optoelectronic devices. Monolayer tungsten diselenide (WSe₂) is a direct-gap semiconductor with a bandgap of ~1.6eV, and is therefore a complement to other two-dimensional materials such as graphene, a gapless semimetal, and boron nitride, an insulator. The direct bandgap distinguishes monolayer WSe₂ from its bulk and bilayer counterparts, which are both indirect gap materials with smaller bandgaps. This sizable direct bandgap in a two-dimensional layered material enables a host of new optical and electronic devices. In this work, a comprehensive analysis of the effect of optical excitation on the transport properties in few-layer WSe₂ is studied. Monolayer WSe₂ flakes from natural WSe₂ crystals were transferred onto Si/SiO₂ (270nm) substrates by mechanical exfoliation. The flakes were observed under an optical microscope. A FET based on mechanically exfoliated WSe₂ was fabricated using photolithography with Molybdenum as metal contact and Silicon as back gate and the electronic properties were measured in a wide range of temperatures. The mobility of our device was found to be 0.2 cm²/V-S at room temperature. The schottky barrier height was found to decrease from 80 meV to 25 meV as the gate voltage increases.