Switching Behavior of a Heterostructure Based on Periodically Doped Graphene Nanoribbon

We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $-0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.

Figure 1

Unit cells of (a) B-doped and (b) N-doped 7-AGNRs with lattice constants 12.87 and 12.78 Å, respectively. The C atoms are denoted by black open circles while the dopant atoms are denoted by blue (B) and red (N) solid circles. The ribbon edges are passivated by hydrogen atoms (green balls). (c) The in-plane heterostructure, where B-AGNR (N-AGNR) is in the left (right) with blue (red) background. We set the interface as $x=0$. A bias voltage $V_b$ gives rise to symmetric potential change $\pm V_b/2$ in the left (right) region. The dashed vertical line denotes the boundary between the left, right electrode and scattering region. Fading black in the electrodes indicates continuation to infinity.

Figure 2

Calculated energy band structures of (a) undoped 7-AGNR, (b) B-AGNR, and (d) N-AGNR from DFT calculations (solid black lines) and via Wannier interpolated tight-binding model (red $\times$ symbols) with the corresponding plots for density of states (DOS) for (b) and (d) in (c) and (e), respectively. The Fermi energy is indicated by the horizontal dotted line and crosses the impurity-induced sub-band, which is pointed out by arrows in (b) and (d). It is noted that we multiply the partial DOS of B and N by ${10}^5$ and $10$, respectively.

Figure 3

(Inset) Potential profile of the interface represented by the smoothstep function $V(x)=(V_b/2)\tanh \left(-2x/\ell \right)$, here the potential $V\left(x\right)$ decreases from $V_b/2$ to $-V_b/2$ over a distance $\ell$ around $x=0$ if $V_b>0$. (Main panel) The corresponding $I$-$V$ curve with various $\ell$. The regions labeled (a)–(c) indicate the three cases of $I$-$V$ curve discussed in the main text.

Figure 4

Band structures of both left and right electrodes with transmission probability in the middle for $\ell =5$, $10$, and $20\mathrm{nm}$ at (a) $V_b=0.1$ and (b) $0.45\mathrm{V}$. The dotted lines indicate the electrochemical potentials of the electrodes and give the bias window (shaded area) in the middle figure. In (a), Fermi–Dirac distribution function $f_{L,R}\left(E,V_b\right)$ versus energy at room temperature (300 K) is also plotted in red dash-dotted line for each electrode with respect to the top $x$ axes.