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

We have investigated the effect of an Al₂O₃passivation layer on the performance of few-layer WS₂FETs. While the performance of WS₂FETs is often limited by a substantial decrease in carrier mobility owing to charged impurities and a Schottky barrier between the WS₂and metal electrodes, the introduction of an Al₂O₃overlayer by atomic layer deposition (ALD) suppressed the influence of charged impurities by high-κdielectric screening effect and reduced the effective Schottky barrier height. We argue that n-doping of WS₂, induced by positive fixed charges formed at Al₂O₃/WS₂interface during the ALD process, is responsible for the reduction of the effective Schottky barrier height in the devices. In addition, the Al₂O₃passivation layer protected the device from oxidation, and maintained stable electrical performance of the WS₂FETs over 57 d. Thus, the ALD of Al₂O₃overlayer provides a facile method to enhance the performance of WS₂FETs and to ensure ambient stability.