Fabrication of Tunneling Field Effect Transistors (TFETs) and the study of graphene

Abstract: After the discovery of graphene in 2004, a single layer of graphite, the assembly of 2D materials became a promising research area in solid state Physics. This thesis explores fabrication of 2D-heterostructures that aim to probe into graphene’s electronic structure with the Tunneling Field Effect Transistor (TFET). In the fabrication process, we used mechanical exfoliation to obtain monolayer graphene and Si-SiO2 as the substrate and back gate of the device. Then, atomically thin hexagonal boron nitride (hBN) was used as the tunneling barrier because of its insulating properties and smooth surface. Gold (Au) leads were evaporated on the devices so that a tunneling current could be extracted from the sample. In this thesis, TFETs are suggested as a complementary alternative to Scanning Tunneling Microscopy (STM) in order to study the electronic properties of 2D materials. Our results showed several spectroscopic features of graphene, some of which could be tuned by an applied gate voltage while others could not . Analysis of the gate tunable spectroscopic feature suggests it may be the Dirac point (E_D), a signature of graphene’s unique band structure. On the other hand, the spectroscopic feature that is insensitive to gate voltage could be attributed to inelastic tunneling processes i.e. a phonon excitation. Future research will be able to use these devices under high magnetic fields (∼ 45T) and low temperatures (∼ 25mK). TFET’s also open the door to an alternative probing method to study the electronic properties of any 2D-material by simply replacing graphene by the desired sample to be studied.