Graphene-based bipolar spin diode and spin transistor: Rectification and amplification of spin-polarized current

Minggang Zeng, Lei Shen (沈雷), Miao Zhou (周苗), Chun Zhang, and Yuanping Feng

Phys. Rev. B 83, 115427 – Published 14 March 2011

Abstract

Using nonequilibrium Green’s function method combined with density functional theory we report bipolar spin diode behavior in zigzag graphene nanoribbons (ZGNRs). Nearly $\pm 100 %$ spin-polarized current can be generated and tuned by a source-drain voltage and/or magnetic configurations in these two-terminal bipolar spin diodes. This unique transport property is attributed to the intrinsic transmission selection rule of the wave function of spin subbands near the Fermi level in ZGNRs. Moreover, the bias voltage and magnetic configurations of the two-terminal ZGNR-based spin diodes provide a rich variety of ways to control the spin current, which can be used to design three-terminal spin transistors. These ZGNRs-based components make possible the manipulation of spin-polarized current such as rectification and amplification for carbon-based spintronics.

Received 8 January 2011

DOI:https://doi.org/10.1103/PhysRevB.83.115427

Authors & Affiliations

Minggang Zeng^1,2, Lei Shen (沈雷)^1,*, Miao Zhou (周苗)¹, Chun Zhang^1,3, and Yuanping Feng^1,†

¹Department of Physics, 2 Science Drive 3, National University of Singapore, Singapore 117542, Singapore
²NanoCore, 5A Engineering Drive 4, National University of Singapore, Singapore 117576, Singapore
³Department of Chemistry, 3 Science Drive 3, National University of Singapore, Singapore 117543, Singapore

^*shenlei@nus.edu.sg
^†phyfyp@nus.edu.sg

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Vol. 83, Iss. 11 — 15 March 2011

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Images

Figure 1
Schematic diagram of ZGNRs-based $bipolar$ spin diodes. An external magnetic field is used to magnetize one or both GNR leads. $M_{L}$ and $M_{R}$ represent the magnetization of the left and right leads under the magnetic field, respectively. The value of $M_{L}$ and $M_{R}$ can be 1, 0, or $- 1$ , corresponding to magnetization along the $+ y$ direction, nonmagnetic lead, and magnetization along the $- y$ direction, respectively. (a) Under a positive bias only spin-down electrons transport through devices. Note that the flow direction of electrons is from right to left leads while the flow direction of current is from left to right leads. (b) Under a negative bias only spin-up electrons are allowed to transport from left to right leads. It behaves as a bias-controlled bipolar spin diode device. The circuit diagram of this bias-controlled bipolar spin diode is shown in the inset.Reuse & Permissions
Figure 2
Spin-dependent transmission spectrum as a function of electron energy $E$ , bias $V_{SD}$ , and $I$ - $V$ curve, respectively, for different spins and under various magnetic configurations of the electrodes. (a) and (b) Spin-up state in the magnetic configuration $[1, 1]$ . (c) and (d) Spin-down state in $[1, 1] .$ (e) and (f) Spin-up state in $[1, - 1] .$ (g) and (h) Spin-down state in $[1, - 1]$ . The up and down triangles shown by the intersecting solid straight lines are the bias windows which sets boundaries for transmission that contributes to the current at a given bias voltage. The Fermi energy is set to zero.Reuse & Permissions
Figure 3
Ribbon width dependence of transmission spectrum and $I$ - $V$ curve showing decrease of both the zero transmission gap (ZTG) and the threshold voltage with the increase of ribbon width.Reuse & Permissions
Figure 4
Spin-dependent transmission spectrum as a function of electron energy $E$ , bias $V_{SD}$ , and $I$ - $V$ curve, respectively, for various spin states and magnetic configurations of the electrodes. (a) and (b) Spin-up state in magnetic configuration $[1, 0] .$ (c) and (d) Spin-down state in $[1, 0]$ . (e) and (f) Spin-up state in $[- 1, 0]$ . (g) and (h) Spin-down state in $[- 1, 0]$ . The up and down triangles shown by the intersecting solid straight lines are the bias windows which sets boundaries for transmission that contributes to the current at a given bias voltage. The Fermi energy is set to zero.Reuse & Permissions
Figure 5
(a) Band structure of the magnetized left lead (left panel), transmission curve (middle panel), and band structure of the nonmagnetic right lead (right panel) of the device shown in Fig. 1 at zero bias. The spin-up bands are shown in blue while the spin-down bands are given in orange. The dashed (solid) line with an arrow illustrates a forbidden (allowed) hopping of electrons from the left lead to the right lead due to the symmetry mismatching (matching) of the $π$ and $π^{*}$ subbands. (b) The same information as (a) but for a positive bias ( $+ 0.4$ V). The transmission gap for spin-down is reduced but that for spin-up is increased compared to that in Figs. 4g and 4g which opens spin-down channel and suppresses spin-up channel as in Figs. 4h and 4f. (c) and (d) Isosurface plots of the $Γ$ -point wave functions of $π^{*}$ and $π$ subbands for 8-ZGNR. Red and blue indicate opposite signs of the wave function.Reuse & Permissions
Figure 6
Schematic illustrations of ZGNR-based transistors with current and voltage amplification functions, respectively. (a)–(c) Top and sideviews of the current-amplifying three-terminal spin-up and spin-down transistors. (d) and (e) The circuit symbols of spin-up and spin-down transistors, respectively. (f) The current gain ( $| I_{C} / I_{B} |$ ) as a function of $V_{B} / V_{C}$ based on Eq. (3). (g) and (h) Top and side views of a Johnson-type transistor as a voltage amplifier.Reuse & Permissions

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