Naveen Kaushik: Impact of charge transfer at the TiO2-MoS2 interface on electron transport in MoS2

posted 3 Jun 2016, 01:34 by Peter Boggild
Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology Bombay

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). 
[2] A. Nipane, D. Karmakar, N. Kaushik, S. Karande and S. Lodha Few Layer MoS2 p-Type Devices Enabled by Selective Doping Using Low Energy Phosphorus Implantation, "accepted for publication in ACS Nano, (2016).
[3] N. Kaushik, D. Karmakar, A. Nipane, S. Karande and S. Lodha Interfacial n-Doping Using an Ultrathin TiO2 Layer for Contact Resistance Reduction in MoS2, "ACS Applied Materials and Interfaces, ACS-AMI, 8 (1), pp 256263, (2016). 

Naveen Kaushik is currently a PhD student in the Department of Electrical Engineering at the Indian Institute of Technology Bombay. His research focuses on contact and doping strategies for transition metal dichalcogenides (TMDs), especially MoS2. He holds an M.Tech in solid state electronic materials from Indian Institute of Technology Roorkee, where he worked on TCAD simulations of FinFET-based SRAM circuits. He was awarded a Prime Minister Fellowship during his PhD given to the top 100 doctoral students by the government of India. He also got the Malhotra Weikfield national award for nanoscience in 2016 for his work done on TMDs.