Giant electron-hole transport asymmetry in ultra-short quantum transistors.
basic_science · Level V
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- Record sourced from PubMed, PMID 28561024.
- Also identified by DOI 10.1038/ncomms15491 and PMC identifier 5460015.
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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 η<sub>e-h</sub>. 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, η<sub>e-h</sub> reaches up to 2.6 for a device with a band gap of 270 meV. The charging energies in this device exceed 100 meV.