Abstract:

We address recent experiments (Science 2009, 325, 1367) reporting on highly efficient multiplication of electron?hole pairs in carbon nanotube photodiodes at photon energies near the carrier multiplication threshold (twice the quasi-particle band gap). This result is surprising in light of recent experimental and theoretical work on multiexciton generation in other confined materials, such as semiconducting nanocrystals. We propose a detailed mechanism based on carrier dynamics and impact excitation resulting in highly efficient multiplication of electron?hole pairs. We discuss the important time and energy scales of the problem and provide analysis of the role of temperature and the length of the diode.

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