Atomic layer deposited Al₂O₃passivation layer for few-layer WS₂field effect transistors

We have investigated the effect of an Al2O3 passivation layer on the performance of few-layer WS2 FETs. While the performance of WS2 FETs is often limited by a substantial decrease in carrier mobility owing to charged impurities and a Schottky barrier between the WS2 and metal electrodes, the introduction of an Al2O3 overlayer by atomic layer deposition (ALD) suppressed the influence of charged impurities by high-κ dielectric screening effect and reduced the effective Schottky barrier height. We argue that n-doping of WS2, induced by positive fixed charges formed at Al2O3/WS2 interface during the ALD process, is responsible for the reduction of the effective Schottky barrier height in the devices. In addition, the Al2O3 passivation layer protected the device from oxidation, and maintained stable electrical performance of the WS2 FETs over 57 d. Thus, the ALD of Al2O3 overlayer provides a facile method to enhance the performance of WS2 FETs and to ensure ambient stability.