Theoretical Study of Graphene Nanoribbon Photo-Detectors

Mahdi Pourfath, Hans Kosina, and Siegfried Selberherr Institute for Microelectronics, TU Wien, Gußhausstraße 27–29/E360, A-1040 Wien, Austria Email: {pourfath|kosina|selberherr}@iue.tuwien.ac.at Graphite-related materials such as carbon nanotubes (CNTs) and graphene have been extensively studied in recent years due to their exceptional electronic, opto-electronic, and mechanical properties. However, the limited control over the chirality and diameter of CNTs and thus of the associated electronic bandgap remains a major technological problem. Recently, graphene sheets have been patterned into narrow nanoribbons [1]. The electronic properties of GNRs exhibit a dependence on the ribbon direction and width. The electronic band structure of GNRs depends on the nature of their edges: zigzag or armchair[2, 3]. In Fig. 1-a, a honeycomb lattice having armchair edges along the x direction is shown. In comparison with CNTs, there are key potential advantages in designing and constructing device architectures based on GNRs [4]. The direct bandgap and the tunability of the relatively narrow bandgap with the ribbon’s width enables them as suitable candidates for opto-electronic devices, especially for infra-red applications. The non-equilibrium Green’s function (NEGF) formalism is used in this work to perform a comprehensive study of photo detectors based on graphene nanoribbons. The device response is studied for a wide range of photon energies. The energy conversion efficiency as a function of the incident photon energy, ribbon’s width, and orientation is evaluated. The atomistic real space tight-binding approach for the description of the electronic bandstructure has been used [5]. For device simulation the Hamiltonian of electron-photon interaction in real space has been employed [6]: