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Barrier-free tunneling in a carbon heterojunction transistor
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View: Figures


Image of FIG. 1.
FIG. 1.

Carbon-based HFET. (a) Schematic band structure at ON (red solid line) and OFF states (blue solid line). Proposed device has a semimetallic zero-band gap region (shaded). and are Fermi levels at the source and the drain, respectively. The dashed lines show the band gap of normal p-i-n structure in the absence of semimetal at ON state. (b) Atomistic configuration of a CNT and GNR heterostructure. (c) Schematic device structure. The channel is a carbon-based heterostructure that consists of a metallic (6,0) CNT and semiconducting a-GNRs. Double-gate geometry with 1.5 nm thick gate oxide . Lengths of source/drain extensions, metallic CNT, gate-controlled channel, and unbiased channel (gate underlap) are , , , and , respectively. Source (drain) GNR is p-doped (n-doped) with doping density, , which is equivalent to 0.1/nm. Effective doping density at the left half of the metallic CNT is . Power supply voltage is .

Image of FIG. 2.
FIG. 2.

(a) characteristics on a log scale (blue curve with left axis) and on a linear scale (green curve with right axis). Red dots indicate several important points such as threshold voltage (c), ON state (d), and OFF states (e) and (f). Subthreshold swing, is shown for various gate bias ranges. It shows an ambipolar conduction by both electrons and holes. Current saturates beyond as a potential hump appears [see the arrow-indicated region in Fig. 2(d)] due to the partial gate structure. (Ref. 11, Fig. S2). The minimum leakage current is shifted to by using appropriate metal work function engineering . (b) plot. The output characteristic is analogous to that of an ordinary transistor except in the low voltage where a tunneling behavior can be clearly observed. (c) Local density-of-states, shown on a log scale, at threshold voltage, . Metallic CNT does not have band gap and states exist at the entire energy levels. The solid lines show the band gap of the semiconducting GNR. The dashed line shows the self-consistent electrostatic solution of where the conduction band and the valence band touch each other within the metallic region. (d) Current spectrum (red strip) at ON state . (e) and (f) Current spectrums (red strips) at OFF states. The different energy levels of the current spectrums indicate a transition from the electron conduction (e, ) to the hole conduction (f, ). (g) Zoom-in plot of the spatial distribution of current as a function of energy for the region shown inside the box of Fig. 2(d) (left). The right panel shows energy-resolved current density. The sharp feature appearing at is due to the resonant tunneling states originating from the barrier profile at this specific voltage. (h) Transmission probability, as a function of energy, , and gate voltage, . The largest value of is 0.9978.

Image of FIG. 3.
FIG. 3.

Effect of doping in the metallic CNT. (a) Band profiles for CNT doping density, (insufficient doping, red dashed lines) and (used in our simulation, blue solid lines). The left half of the metallic CNT is doped to reduce the inherent band bending at the heterojunction. Red strip shows current spectrum for at . (b) Energy-resolved current density at .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Barrier-free tunneling in a carbon heterojunction transistor