Band structure study of graphene and transition metal dichalcogenides heterostructures

Abstract

According to Moore’s Law, it is predicted that the number of transistors –the building blocks of any modern electronic device– on integrated circuits per square inch will double every year. However studies show that the limit would be reached within the next three years as the size of Silicon based transistors, already reduced to a few tens of nanometers, can no longer be further reduced. This is not the only challenge for the semiconductor industry. Besides the transistor size, engineers are also not being able to decrease the minimum voltage required to turn on a device, making it tough for us to build even low power consuming devices. This has compelled us to focus on different alternatives. Graphene has turned out to be the wonder material in the scientific community recently, and its applications are innumerable. It is only an atomically thick 2 dimensional material with very high electron mobility. However, the only reason that acts as the barrier to fully utilize the great potential of this material is its missing band gap. This is when the role of transition metal dichalcogenides (TMDCs) comes into play, another atomically thick 2 dimensional set of materials, which, unlike Graphene, has direct band gap but low mobility i.e. characteristics that can compensate for those missing in Graphene. Scientists have recently combined Graphene with TMDCs to extract the best possible characteristics from both the materials in quest for a substitution for traditional Silicon based transistors in the industry and the results are promising; however, the low current on/off ratio of such devices is still a challenge that needs to be overcome. In our thesis we have simulated band structures of Graphene and different TMDCs like MoS2, MoT e2 etc. Additionally we have simulated band structures of Graphene interfaced with various TMDCs and also Graphene sandwiched between various TMDCs. Through literature review, we have also found out the spin orbit coupling – a phenomenon that allows us to control electricity through orientation of electrons’ polarization rather than the flow of charge – of Graphene and various TMDCs. We have then graphically analyzed our data and finally proposed that by combining the electronic band gap and the spin orbit coupling of a material simultaneously in the future, we may be able to create devices which will be much smaller in size and run with much lower power than current transistors and simultaneously have a high current on/off ratio.