Plasma-Enhanced Atomic Layer Deposition of HfO₂ on Monolayer, Bilayer, and Trilayer MoS₂ for the Integration of High-κ Dielectrics in Two-Dimensional Devices

As two-dimensional (2D) electronic devices continue to advance, the need for integrating high-quality, high-κ nanoscale dielectrics becomes more essential. Plasma-enhanced atomic layer deposition (PEALD) is a promising approach for depositing ultrathin dielectrics directly onto the surface of 2D materials. However, the mechanism for PEALD film growth on the van der Waals materials, along with the impact of the plasma process on structural and interfacial properties of 2D materials, has not been fully explored. In this work, we demonstrate the effects of the plasma process on monolayer, bilayer, and trilayer MoS2. Back-gated MoS2 transistors of varying thickness were tested before and after ALD/PEALD HfO2, and it was verified that plasma damage does occur, predominantly in the surface layer of the MoS2, leading to significantly greater impact in monolayers. By increasing the thickness of the MoS2, the adverse effects of the plasma process are reduced appreciably. This observation is further supported by Raman and transmission electron microscopy analysis. In addition to providing information about defect generation and morphology, this study provides key insights into the charge transfer between HfO2 and MoS2. Overall, this detailed analysis of the impact of the PEALD plasma process on MoS2 contributes to the reliable integration of ultrathin, high-κ dielectrics in 2D devices.