Conformal bilayer h-AlN epitaxy on WS₂ by ALD with ultralow leakage current

In this work, we develop an ultrathin epitaxial h-AlN as an interfacial layer (IL) between HfO₂ and monolayer WS₂ channel by atomic layer deposition (ALD). The growth of ultrathin dielectrics using ALD has been challenging due to the dangling-bond-free surface of 2D materials. By utilizing sub-1 nm h-AlN as an IL and depositing HfO₂ high-k dielectric, we were able to form a uniform and atomically flat gate dielectric without voids. The resulting structure exhibits an equivalent oxide thickness as low as 1 nm and ultra-low leakage currents of ∼10⁻⁶ A/cm². The fabricated top-gate WS₂ transistors demonstrate on-off ratios of around 10⁶ and subthreshold swing as low as 93 mV/dec. Furthermore, we have verified the feasibility of using h-AlN IL for a gate-all-around structure. Our work presents a CMOS-compatible low-temperature ALD process for integrating gate dielectrics, offering excellent thickness scalability and uniform coverage around monolayer WS₂ nanosheets. The combination of high-quality two-dimensional dielectrics and semiconductors will contribute to the development of future high-performance and low-power electronic devices.