Molybdenum disulfide (MoS2) has attracted significant research interest due to its sizable bandgap and ultrathin nature. However, high contact resistance [1] and lack of methods for chemical doping, especially p-type [2], have emerged as fundamental bottlenecks for devices based on MoS2. 

In this work we demonstrate a novel technique to lower the contact resistance on MoS2 by introducing an ultrathin TiO2 layer between metal and MoS2 [3]. The reduction in contact resistance and constant Schottky barrier height was attributed to an increased n-type doping at metal-MoS2 contact. Interfacial doping has been validated by first-principles calculations, showing the metallic behavior of the TiO2-MoS2 interface due to inter-layer charge transfer and associated interfacial strain. Electrical and materials studies also show that TiO2 increases the charge density in the MoS2 layer underneath which results in improved transistor on-current besides nearly contact resistance-free field effect mobility. In summary, this work presents a significant advance in contact engineering of transition metal dichalcogenides by enabling contact resistance reduction through interfacial n-type doping of MoS2. Unlike other doping techniques reported previously, this is an air stable and area selective technique that allows doping of different transistor regions such as contact and channel separately.

[1] N. Kaushik, A. Nipane, F. Basheer, S. Dubey, S. Grover, M. Deshmukh and S. Lodha Schottky barrier heights for Au and Pd contacts to MoS2, "Applied Physics Letters, 105, 113505 (2014).