Electron transport through quantum-dot states of n-type carbon nanotubes

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We calculate electron transmission in carbon nanotube field-effect-transistors, based on a tight-binding model. For positive gate voltages, a quantum dot is formed in the nanotube between two regions doped p type by metal contacts, and the resulting quantum dot states give rise to n-type conduction. While p-type currents for negative gate voltages exhibit robustness, n currents sensitively depend on the depletion layer between regions doped p type by the contacts and n type by the gate. This feature explains the polarity of electron transport observed in carbon nanotube transistors.