Batch-Fabricated WSe-on-Sapphire Field-Effect Transistors Grown by Chemical Vapor Deposition

Stepper-based batch fabrication of top-gated field-effect transistors (FETs) is demonstrated on few-layer WSe₂-on-sapphire grown by chemical vapor deposition. This article reports the electrical characterization of 94 transistors with three different transistor structures. ON-/ OFF-current ratios exceeding 10⁵ at room temperature with noise-floor-limited gate current and contact-limited ON-current density of 15 nA/ \mu \text{m} was achieved for FETs using a structure in which the gate overlaps the source and drain contacts. Two transistors with open channel access regions are used to allow ion doping through polyethylene oxide: cesium perchlorate (PEO: CsClO₄) to induce electron and hole conductivity and allow characterization of the intrinsic FET characteristics. In these geometries, the ON-current increased by four orders of magnitude with ON-/ OFF-current ratio greater than 10⁶ at {V}_{\text {DS}} = -0.05 V, compared to gate overlapped FETs. An analytic 2-D FET model was used to model the full current-voltage characteristics. This allowed the field-effect mobility to be extracted revealing the gate and drain field dependence for the first time. The fit of the measured characteristics from subthreshold to saturation is made with only four fitting parameters, revealing a field-dependent electron mobility ranging from 1 to 2.6 cm²/Vs.