In-situ growth of HfO2 on clean 2H-MoS2 surface: Growth mode, interface reactions and energy band alignment.

Room temperature growth of HfO 2 thin film on clean 2H-MoS 2 via plasma-sputtering of Hf-metal target in an argon/oxygen environment was studied in-situ using x-ray photoelectron spectroscopy (XPS). The deposited film was observed to grow akin to a layer-by-layer growth mode. At the onset of growth, a mixture of sulfate- and sulfite-like species (SO x 2− where x = 3, 4), and molybdenum trioxide (MoO 3 ), are formed at the HfO 2 /MoS 2 interface. An initial decrease in binding energies for both Mo 3d and S 2p core-levels of the MoS 2 substrate by 0.4 eV was also observed. Their binding energies, however, did not change further with increasing HfO 2 thickness. There was no observable change in the Hf4f core-level binding energy throughout the deposition process. With increasing HfO 2 deposition, MoO 3 becomes buried at the interface while SO x 2− was observed to be present in the film. The shift of 0.4 eV for both Mo 3d and S 2p core-levels of the MoS 2 substrate can be attributed to a charge transfer from the substrate to the MoO 3 /SO x 2− -like interface layer. Consequently, the Type I heterojunction valence band offset (conduction band offset) becomes 1.7 eV (2.9 eV) instead of 1.3 eV (3.3 eV) expected from considering the bulk HfO 2 and MoS 2 valence band offset (conduction band offset). The formation of these states and its influence on band offsets will need to be considered in their device applications. [ABSTRACT FROM AUTHOR]