Normally Off WSe₂ Nanosheet-Based Field-Effect Transistors with Self-Aligned Contact Doping

Abstract

Despite the advantages of ambipolar semiconductors, high offcurrents and narrow off-state bias window limit their application in enhancementmode field-effect transistors (FETs). We demonstrate the normally off operation of a low-dimensional ambipolar WSe 2 semiconductor FET by forming the lateral p−n homojunction. The self-aligned n-doping of the ambipolar WSe 2 was obtained by intentionally forming Se vacancy via mild Ar-ion treatment. The UV-ozoneassisted growth of the WO X layer increased the hole concentrations of the WSe 2 channel, where its high work function makes the underlying WSe 2 electrondeficient. A high on/off ratio of ∼10 8 and a wide off-range gate bias with the normally off operation were obtained in the n−p−n nanostructured WSe 2 FETs, which was also characterized by photocurrent mapping analysis. The electrical characteristics of the devices exhibited their thermal stability up to an operating temperature of 140 °C, which was enabled by the formation of the p−n homojunction barrier. High on/off ratios, wide off-range bias, and decent field-effect carrier mobility of the normally off nanosheetbased WSe 2 FET were well maintained at elevated temperatures, which indicates that the low-dimensional ambipolar semiconductor with a junction barrier can play a pivotal role in the next-generation device architecture.