High performance top-gated multilayer WSe₂ field effect transistors

In this paper, high performance top-gated WSe₂ field effect transistor (FET) devices are demonstrated via a two-step remote plasma assisted ALD process. High-quality, low-leakage aluminum oxide (Al₂O₃) gate dielectric layers are deposited onto the WSe₂ channel using a remote plasma assisted ALD process with an ultrathin (∼1 nm) titanium buffer layer. The first few nanometers (∼2 nm) of the Al₂O₃ dielectric film is deposited at relatively low temperature (i.e. 50 °C) and remainder of the film is deposited at 150 °C to ensure the conformal coating of Al₂O₃ on the WSe₂ surface. Additionally, an ultra-thin titanium buffer layer is introduced at the WSe₂ channel surface prior to ALD process to mitigate oxygen plasma induced doping effects. Excellent device characteristics with current on-off ratio in excess of 10⁶ and a field effect mobility as high as 70.1 cm² V^-1 s^-1 are achieved in a few-layer WSe₂ FET device with a 30 nm Al₂O₃ top-gate dielectric. With further investigation and careful optimization, this method can play an important role for the realization of high performance top gated FETs for future optoelectronic device applications.