Effect of Au/HfS₃ interfacial interactions on properties of HfS₃-based devices

X-ray photoemission spectroscopy (XPS) has been used to examine the interaction between Au and HfS₃ at the Au/HfS₃ interface. XPS measurements reveal dissociative chemisorption of O₂, leading to the formation of an oxide of Hf at the surface of HfS₃. This surface hafnium oxide, along with the weakly chemisorbed molecular species, such as O₂ and H₂O, are likely responsible for the observed p-type characteristics of HfS₃ reported elsewhere. HfS₃ devices exhibit n-type behaviour if measured in vacuum but turn p-type in air. Au thickness-dependent XPS measurements provide clear evidence of band bending as the S 2p and Hf 4f core-level peak binding energies for Au/HfS₃ are found to be shifted to higher binding energies. This band bending implies formation of a Schottky-barrier at the Au/HfS₃ interface, which explains the low measured charge carrier mobilities of HfS₃-based devices. The transistor measurements presented herein also indicate the existence of a Schottky barrier, consistent with the XPS core-level binding energy shifts, and show that the bulk of HfS₃ is n-type.