Three-terminal carbon nanotube junctions: Current-voltage characteristics

A T-type three-terminal junction made of two as-grown semiconducting single-walled carbon nanotubes was fabricated with two electrodes attached to each terminal. It is found that the symmetric current-voltage characteristic along one nanotube can be turned to asymmetric by applying a voltage to the second nanotube acting as a local gate electrode—a property that can be used to form only nanotube-based transistors and amplifiers. Our analysis shows that an asymmetric geometry is essential for devices of this kind to exhibit such a function. More significant rectification behavior has also been observed across the end-bulk junction of the two nanotubes in the presence of a negative backgate voltage.

Figure 1

Scanning electron microscope (SEM) micrograph of a three-terminal junction contacted by two $\mathrm{Ti}∕\mathrm{Au}$ electrodes at each terminal. The numbers in the image represent the electrodes for electrical measurement. The nanotube length between electrodes 2 and 3 is about $1.5\mu \mathrm{m}$ and between electrode 5 and the junction is about $1.3\mu \mathrm{m}$.

Figure 2

Characterization of the nanotubes by examining on each of them the backgate voltage $\left(V_{\mathit{bg}}\right)$ dependence of the current induced by a fixed bias voltage of $100\mathrm{mV}$ at $100\mathrm{K}$. The results show that both nanotubes are $p$-type semiconductors.

Figure 3

(Color online) The rectification effect across the junction at (a) $200\mathrm{K}$ and (b) $100\mathrm{K}$. The $I_{3,5}\text{−}{V}_{\mathit{\text{bias}}}$ curve is nearly symmetric at zero backgate voltage, as shown in the inset in the upper frame, but it becomes highly asymmetric at a backgate voltage of $-1\mathrm{V}$. The inset in the lower frame shows that the current suppression at negative bias can sustain to $-1.5\mathrm{V}$ at $100\mathrm{K}$.

Figure 4

(Color online) The current in the first nanotube (connected to electrodes 2 and 3) can be influenced by the voltage applied to the second nanotube which acts as a local gate electrode. (a) $I_{2,3}$ as a function of $V_5$ at $100\mathrm{K}$ and $500\mathrm{mV}$ bias voltage, in the absence of backgate voltage. (b) $I_{2,3}\text{−}{V}_{\mathit{\text{bias}}}$ at $100\mathrm{K}$ for different $V_5$ of $-1\mathrm{V}$, $0\mathrm{V}$, and $1\mathrm{V}$, respectively. The inset shows the schematic of experiment.

Figure 5

(a) Schematic energy bands of a metal electrode and a semiconducting carbon nanotube under a reverse bias voltage and in the presence of a negative local gate voltage applied from the second nanotube to the first one near the positively biased electrode. (b) Proposed $p\text{−}p$ isotype heterojunction made of two dissimilar semiconducting carbon nanotubes under equilibrium (solid lines) and a forward bias voltage (dashed lines). The dot-dashed line represents the position of Fermi level $E_F$ at equilibrium. The wide gap and the narrow gap correspond to the small-diameter nanotube and the large-diameter nanotube, respectively.

Figure 6

(Color online) $I_{3,5}\text{−}{V}_{\mathit{\text{bias}}}$ characteristics under forward bias voltages, together with the fitting curves at $50\mathrm{K}$, $100\mathrm{K}$, and $200\mathrm{K}$. The current is in a logarithmic scale.