Abstract
Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies. Here we report ultra-clean 10 to 100 nm scale suspended nanotube transistors with a large electron-hole transport asymmetry. The devices consist of naked nanotube channels contacted with sections of tube under annealed gold. The annealed gold acts as an n-doping top gate, allowing coherent quantum transport, and can create nanometre-sharp barriers. These tunnel barriers define a single quantum dot whose charging energies to add an electron or a hole are vastly different (e−h charging energy asymmetry). We parameterize the e−h transport asymmetry by the ratio of the hole and electron charging energies ηe−h. This asymmetry is maximized for short channels and small band gap tubes. In a small band gap device, we demonstrate the fabrication of a dual functionality quantum device acting as a quantum dot for holes and a much longer quantum bus for electrons. In a 14 nm-long channel, ηe−h reaches up to 2.6 for a device with a band gap of 270 meV. The charging energies in this device exceed 100 meV.
Highlights
Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies
An important feature of ultra-clean single-walled carbon nanotube (SWCNT) channels is that a small gate voltage can tune them from n-type to p-type devices
Quantum SWCNT devices can be engineered to create an e À h transport asymmetry. This is achieved for instance in SWCNT quantum dot (QD) transistors whose tunnel barrier heights depend on whether the channel is n- or p-doped
Summary
Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies. The annealed gold acts as an n-doping top gate, allowing coherent quantum transport, and can create nanometre-sharp barriers These tunnel barriers define a single quantum dot whose charging energies to add an electron or a hole are vastly different (e À h charging energy asymmetry). A large e À h transport asymmetry in SWCNT transistors could allow them to act as both active logic elements (QDs) for hole doping and interconnects (quantum bus) for electron doping This dual functionality is needed to create reconfigurable logic circuits which can be programmed with gate voltages[16] and would support the development of commercial SWCNT electronics[17]. The charging energies of our shortest device (Device B) exceed 100 meV, demonstrating the potential for room temperature operation
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