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Title: Photocurrent spectroscopy of exciton and free particle optical transitions in suspended carbon nanotube pn-junctions

We study photocurrent generation in individual, suspended carbon nanotube pn-junction diodes formed by electrostatic doping using two gate electrodes. Photocurrent spectra collected under various electrostatic doping concentrations reveal distinctive behaviors for free particle optical transitions and excitonic transitions. In particular, the photocurrent generated by excitonic transitions exhibits a strong gate doping dependence, while that of the free particle transitions is gate independent. Here, the built-in potential of the pn-junction is required to separate the strongly bound electron-hole pairs of the excitons, while free particle excitations do not require this field-assisted charge separation. We observe a sharp, well defined E{sub 11} free particle interband transition in contrast with previous photocurrent studies. Several steps are taken to ensure that the active charge separating region of these pn-junctions is suspended off the substrate in a suspended region that is substantially longer than the exciton diffusion length and, therefore, the photocurrent does not originate from a Schottky junction. We present a detailed model of the built-in fields in these pn-junctions, which, together with phonon-assistant exciton dissociation, predicts photocurrents on the same order of those observed experimentally.
Authors:
 [1] ; ; ; ;  [2] ;  [1] ;  [3] ;  [3]
  1. Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States)
  2. Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States)
  3. (United States)
Publication Date:
OSTI Identifier:
22489064
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 107; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CARBON NANOTUBES; DIFFUSION LENGTH; ELECTRIC CONTACTS; EXCITATION; EXCITONS; JUNCTION DIODES; PHONONS; PHOTOCURRENTS; P-N JUNCTIONS; POTENTIALS; SPECTRA; SPECTROSCOPY; SUBSTRATES