• graphene top-gate THz terahertz

This Master thesis (Tesi di Laurea Magistrale) is aimed at the design and test of a graphene-based Terahertz photodetector. We exploit the high-mobility of graphene to fabricate a top-gated Graphene Field Effect Transistor (GFET) that is able to detect THz radiation. The photodetection theory was originally developed by M. Dyakonov and M. S. Shur in 1993 and it is based on the nonlinear transport properties of semiconductor FETs and GFETs, which lead to the rectification of an ac current induced by the incoming radiation. The efficiency of the detector is directly linked to the carrier mobility, which can be quite low in traditional semiconductor FETs at room temperature. On the contrary, graphene shows extremely high-mobilities most independently of temperarute which makes it a promising material for a wide range of applications.
In our approach the modulation of the carrier density in the graphene channel is achieved through a metallic top gate, isolated from graphene by a thin layer of Hafnium Oxide that we deposit using Atomic Layer Deposition (ALD). In addition, we exploit integrated log-periodic antennas in order to enhance the coupling between the incident THz wave and the graphene transistor. We successfully detected radiation at 0.3 THz at room temperature, both with monolayer and bilayer graphene devices. We achieved a maximum responsivity of 0.09 V/W and a minimum Noise Equivalent Power (NEP) of 7\times10^{-8}\,\mathrm{W/\sqrt{Hz}}
. To our knowledge, this work presents the first THz FET photodetector based on graphene.