Scrutinizing pre- and post-device fabrication properties of atomic layer deposition WS₂ thin films

In this work, we investigate the physical and electrical properties of WS₂ thin films grown by a plasma-enhanced atomic layer deposition process, both before and after device fabrication. The WS₂ films were deposited on thermally oxidized silicon substrates using the W(NMe₂)₂(NtBu)₂ precursor and a H₂S plasma at 450 °C. The WS₂ films were approximately 8 nm thick, measured from high-resolution cross-sectional transmission electron imaging, and generally exhibited the desired horizontal basal-plane orientation of the WS₂ layers to the SiO₂ surface. Hall analysis revealed a p-type behavior with a carrier concentration of 1.31 × 10¹⁷ cm⁻³. Temperature-dependent electrical analysis of circular transfer length method test structures, with Ni/Au contacts, yielded the activation energy (E_a) of both the specific contact resistivity and the WS₂ resistivity as 100 and 91 meV, respectively. The similarity of these two values indicates that the characteristics of both are dominated by the temperature dependence of the WS₂ hole concentration. Change in the material, such as in sheet resistance, due to device fabrication is attributed to the chemicals and thermal treatments associated with resist spinning and baking, ambient and UV exposure, metal deposition, and metal lift off for contact pad formation.