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Register a new userFirst Principle-based Analysis of Single-Walled Carbon Nanotube and Silicon Nanowire Junctionless Transistors
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Junctionless transistors made of silicon have previously been demonstrated experimentally and by simulations. Junctionless devices do not require fabricating an abrupt source-drain junction and thus can be easier to implement in aggressive geometries. In this paper, we explore a similar architecture for aggressively scaled devices with the channel consisting of doped carbon nanotubes (CNTs). Gate all around (GAA) field effect transistor (FET) structures are investigated for n- and p-type doping. Current-voltage characteristics and sub-threshold characteristics for a CNTbased junctionless FET is compared with a junctionless silicon nanowire (SiNW) FET with comparable dimensions. Despite the higher on-current of the CNT channels, the device characteristics are poorer compared to the silicon devices due to the smaller CNT band gap.
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We describe a method to fabricate clean suspended single-wall carbon nanotube (SWCNT) transistors hosting a single quantum dot ranging in length from a few 10s of nm down to $approx$ 3 nm. We first align narrow gold bow-tie junctions on top of individual SWCNTs and suspend the devices. We then use a feedback-controlled electromigration to break the gold junctions and expose nm-sized sections of SWCNTs. We measure electron transport in these devices at low temperature and show that they form clean and tunable single-electron transistors. These ultra-short suspended transistors offer the prospect of studying THz oscillators with strong electron-vibron coupling.
Using the first-principles spin density functional approach, we have studied magnetism of a new type of all-carbon nanomaterials, i.e., the carbon nanowires inserted into the single-walled carbon nanotubes. It is found that if the 1D carbon nanowire density is not too higher, the ferromagnetic ground state will be more stable than the antiferromagnetic one, which is caused by weak coupling between the 1D carbon nanowire and the single-walled carbon nanotube. Also, both dimerization of the carbon nanowire and carbon vacancy on the tube-wall are found to enhance the magnetic moment of the composite.
Chirality-selected single-walled carbon nanotubes (SWCNTs) ensure a great potential of building ~1 nm sized electronics. However, the reliable method for chirality-selected SWCNT is still pending. Here we present a theoretical study on the SWCNTs chirality assignment and control during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of the pentagon formation during SWCNT nucleation. Therefore, chirality is randomly assigned on a liquid catalyst surface. Furthermore, based on the understanding, two potential methods of synthesizing chirality-selected SWCNTs are proposed: i) by using Ta, W, Re, Os, or their alloys as solid catalysts, and ii) by changing the SWCNTs chirality frequently during the growth.
We characterize radio frequency detection in a high-quality metallic single-walled carbon nanotube. At a bath temperature of 77 K, only bolometric (thermal) detection is seen. At a bath temperature of 4.2 K and low bias current, the response is due instead to the electrical nonlinearity of the non-ohmic contacts. At higher bias currents, the contacts recover ohmic behavior and the observed response agrees well with the calculated bolometric responsivity. The bolometric response is expected to operate at terahertz frequencies, and we discuss some of the practical issues associated with developing high frequency detectors based on carbon nanotubes.
While decreasing the oxide thickness in carbon nanotube field-effect transistors (CNFETs) improves the turn-on behavior, we demonstrate that this also requires scaling the range of the drain voltage. This scaling is needed to avoid an exponential increase in Off-current with drain voltage, due to modulation of the Schottky barriers at both the source and drain contact. We illustrate this with results for bottom-gated ambipolar CNFETs with oxides of 2 and 5 nm, and give an explicit scaling rule for the drain voltage. Above the drain voltage limit, the Off-current becomes large and has equal electron and hole contributions. This allows the recently reported light emission from appropriately biased CNFETs.
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