Effects of atmospheric UV-O₃ exposure of WSe₂ on the properties of the HfO₂/WSe₂ interface

Transition metal dichalcogenides (TMDCs), such as semiconducting WSe₂, are typically interfaced with a high-quality dielectric layer in device applications. The unreactive basal plane of TMDCs makes the standard technique for deposition of dielectric oxides, atomic layer deposition (ALD), challenging on TMDC surfaces. In this work, we make use of atmospheric ultraviolet–ozone (UV-O₃) exposure of WSe₂ to functionalize its surface and promote uniform ALD of HfO₂. We report two classifications depending on the UV-O₃ exposure time. Low exposures do not result in detectable WSe₂ surface oxidation, while high exposures result in a self-limiting and amorphous tungsten oxyselenide top layer. Following ALD of HfO₂, low exposure samples have an abrupt HfO₂/WSe₂ interface with no interfacial oxide, while high exposure results in an interfacial WO₃ layer between the HfO₂ and the WSe₂, as well as evidence of two doping states observed in the underlying WSe₂. Despite differences in the interface chemistry, both low and high exposures result in uniform and smooth HfO₂ films directly deposited by ALD and a reduction in gate leakage through this HfO₂ layer. We report that our atmospheric UV-O₃ exposure technique on WSe₂ is an avenue for allowing direct ALD of thin uniform oxide films on WSe₂, and the UV-O₃ exposure time provides unique tunability and flexibility in interface design within devices.