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

Abstract

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.