Photodetectors with armchair graphene nanoribbons and asymmetric source and drain contacts

Graphical abstract: - Highlights: • Photodetectors having a-GNR channels of 30 unit cells long and 10 C-atoms wide and asymmetric source and drain electrodes (i.e., p-type and n-type metal-contacted graphenes) are assumed. • Due to the finite potential step induced between such asymmetric electrodes, these types of photodetectors are shown to generate photocurrents under for zero external biases, when illuminated by monochromatic lights in the solar blind UV region (3–5 eV) with quantum efficiencies of ∼27.5–60%. • Numerical simulations also show responsivities for these photodetectors for zero applied biases are about 10.4–13.4 A/mW. • The local photocurrents across the a-GNR channel connected between Au/G (p-type source) and Ti/G (n-type drain) electrodes are shown to be concentrated near the source and drain terminals inside the channel, for V_GS = 0 and V_DS = 0. For |V_GS| > 0, local current peaks move away from the electrodes boundaries. • While for V_GS > 0 negative and positive local currents are concentrated near the source and drain regions, respectively. The current polarities alter for V_GS < 0. • At the maximum of the total photocurrent, polarities of local photocurrent change. • The total currents versus V_DS, obtained under illumination and for V_GS = 0, shift toward negative current values, with respect to the dark current for the same biasing condition. - Abstract: Characteristics of photodetectors with asymmetric source and drain contacts and armchair graphene nanoribbons (a-GNR) channel under monochromatic illuminations of various incident energies in the range of mid infrared (0.1 eV) to solar blind ultra violet (10 eV) are simulated. Simulations show the photocurrent spectrum for the device with an a-GNR of 30 unit cells long and 10 C-atoms wide connected between asymmetric leads made of Au-contacted and Ti-contacted graphenes, under monochromatic illumination of incident intensity 10³ W/cm², exhibits a peak current of 1.897 μA. This peak that is obtained in absence of any external biases, applied to the device terminals, occurs at the energy E = 5.02 eV and correspond to the quantum efficiency of 60%. The evaluated responsivity for this photodetector under zero applied biases equals 13.4 A/mW. The negative and positive local photocurrents are shown peak near the p-type source-channel and n-type drain-channel boundaries under negative gate to source voltages, respectively. Polarities of the local photocurrents alter when the gate-source voltage approaches to the Dirac point, for which the maximum total photocurrent is achieved. Finally, the total device current versus the drain-source voltages obtained under monochromatic illumination, for V_GS = 0, is shown to shift toward negative values in comparison the dark current. This is because the dark current and photocurrents flow in opposite directions. Simulations are performed, using the non-equilibrium Green's function (NEGF) formalism coupled to Poisson solver