Origins of Fermi-Level Pinning between Molybdenum Dichalcogenides (MoSe2, MoTe2) and Bulk Metal Contacts: Interface Chemistry and Band Alignment

Nanometer-scale films of contact metals (Au, Ir, Cr, and Sc), deposited on bulk, exfoliated MoSe2 and MoTe2 by electron beam evaporation under high vacuum (HV, <2 x 10(-6) mbar) and ultrahigh vacuum (UHV, <2 x 10(-9) mbar), are compared to elucidate the metal-transition metal dichalcogenide (TMD) interface chemistry and its relationship with the reactor ambient. Au does not react with MoSe2 but does react with MoTe2, regardless of reactor ambient. In contrast, the presence of an intermetallic is detected at the Ir-MoSe2 and Ir-MoTe2 interfaces when it is deposited in UHV and HV. The typically more reactive, low-work function metals Cr and Sc completely reduce the TMD near the interface. Sc is completely oxidized during metallization in HV. These results highlight the reactive nature of interfaces formed between Mo-based TMDs and metals. Furthermore, band alignment between Au, Ir, and Sc and the Mo-based TMDs deviates significantly from the Schottky-Mott rule. These results elucidate the true chemistry of selected contact metal-TMD interfaces and the oxidizing effects that a higher deposition chamber base pressure has on the interface chemistry. Additionally, our work highlights the need to consider the true interface chemistry when engineering and modeling metal contacts to MoSe2 and MoTe2.