Electric field induced enhancement of photovoltaic effects in graphene nanoribbons

The terahertz (THz) to visible irradiation induced current in zigzag and armchair graphene nanoribbons were investigated by focusing on the modulation of the photovoltaic effects by tuning the electric field ($E$) strength. The numerical results show that spin photovoltaic effects in zigzag-edged graphene nanoribbons can be significantly improved by enhancing the $E$ strength. In detail, an acceptable broadband photoresponsivity with a full optical spin polarization in a broad range of photon energies, including the THz region, can be obtained that can be preserved in the presence of the edge roughness. Furthermore, armchair-edged graphene nanoribbons could reveal a tunable photoresponsivity induced by THz to ultraviolet wavelengths. These results could lead to the enhancement of photovoltaic effects and especially the generation of a spin-polarized photocurrent in all-carbon junctions.

Figure 1

(a) A schematic representation of the proposed nanodevice based on GNRs illuminated with linear radiation with a polarization that is parallel to the channel direction. (b) A schematic representation of nZGNR ($n=6$ denotes the number of zigzag chains along the width direction) under a transverse electric field. The dotted-line rectangle box denotes the ZGNR unit cell.

Figure 2

Spin-resolved band structures of the ZGNR with (a) $E=0$, (b) 0.2, (c) 0.5, and (d) $0.8\mathrm{V}/\mathrm{nm}$. The red (solid) and blue (dash-dotted) lines denote bands of $\alpha$-spin and $\beta$-spin states, respectively. The first important allowable spin-conserved transitions are marked (${\varepsilon }_F$ is set to zero).

Figure 3

Spin-dependent quantum efficiency as a function of the incident photon energy for the spin-photovoltaic device based on ZGNR under the simultaneous effect of linear illumination and a transverse electric field with the strength of (a) $E=0.2$, (b) 0.5, and (c) $0.8\mathrm{V}/\mathrm{nm}$.

Figure 4

The optical spin polarization of the proposed spin-photovoltaic device based on the ZGNR versus the photon energy for various $E$ strengths.

Figure 5

(a) Schematic diagrams of the defective ZGNR under the effect of a transverse electric field. The rectangle box drawn with a dotted line denotes a supercell of the ZGNR. (b) and (c) show the spin-resolved band structures of the defective ZGNR with $E=0$ and $0.2\mathrm{V}/\mathrm{nm}$, respectively. The red (solid) and blue (dash-dotted) lines denote the bands of $\alpha$-spin and $\beta$-spin states, respectively.

Figure 6

(a) The spin-dependent quantum efficiency as a function of the incident photon energy for the spin-photovoltaic device based on the defective ZGNR under the simultaneous effect of linear illumination and the transverse electric field of the strength $E=0.2\mathrm{V}/\mathrm{nm}$. (b) The optical spin polarization of the proposed spin-photovoltaic device based on the defective ZGNR vs the photon energy for $E=0.2\mathrm{V}/\mathrm{nm}$.

Figure 7

[(a) and (b)] Band structures of AGNR with $E=0$, 4, and $8\mathrm{V}/\mathrm{nm}$ (${\varepsilon }_F$ is set to zero). (c) Quantum efficiencies of the photovoltaic device based on AGNR as a function of the incident photon energy under the simultaneous effect of linear illumination and a transverse electric field.