Defect-Dominated Doping and Contact Resistance in MoS₂

Achieving low resistance contacts is vital for the realization of nanoelectronic devices based on transition metal dichalcogenides. We find that intrinsic defects in MoS₂ dominate the metal/MoS₂ contact resistance and provide a low Schottky barrier independent of metal contact work function. Furthermore, we show that MoS₂ can exhibit both n-type and p-type conduction at different points on a same sample. We identify these regions independently by complementary characterization techniques and show how the Fermi level can shift by 1 eV over tens of nanometers in spatial resolution. We find that these variations in doping are defect-chemistry-related and are independent of contact metal. This raises questions on previous reports of metal-induced doping of MoS₂ since the same metal in contact with MoS₂ can exhibit both n- and p-type behavior. These results may provide a potential route for achieving low electron and hole Schottky barrier contacts with a single metal deposition

HfO₂ on MoS₂ by Atomic Layer Deposition: Adsorption Mechanisms and Thickness Scalability

We report our investigation of the atomic layer deposition (ALD) of HfO₂ on the MoS₂ surface. In contrast to previous reports of conformal growth on MoS₂ flakes, we find that ALD on MoS₂ bulk material is not uniform. No covalent bonding between the HfO₂ and MoS₂ is detected. We highlight that individual precursors do not permanently adsorb on the clean MoS₂ surface but that organic and solvent residues can dramatically change ALD nucleation behavior. We then posit that prior reports of conformal ALD deposition on MoS₂ flakes that had been exposed to such organics and solvents likely rely on contamination-mediated nucleation. These results highlight that surface functionalization will be required before controllable and low defect density high-κ/MoS₂ interfaces will be realized. The band structure of the HfO₂/MoS₂ system is experimentally derived with valence and conduction band offsets found to be 2.67 and 2.09 eV, respectively