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Proceedings Paper

Picosecond transient photoconductivity in organic molecular crystals
Author(s): Frank A. Hegmann; Oksana Ostroverkhova; Jianbo Gao; Lloyd Barker; Rik R. Tykwinski; John E. Bullock; John E. Anthony
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Paper Abstract

We examine ultrafast photoconductivity in functionalized pentacene single crystals using optical-pump terahertz-probe techniques. The 0.5 ps rise time observed in the photoconductive transients, which is limited by the response time of the terahertz pulse setup, suggests that mobile charge carriers are a primary photoexcitation. The peak of the photoconductive signal increases as the temperature decreases due to higher carrier mobilities at lower temperatures. A lower limit for the carrier mobility of 1.6 cm2/Vs at 10 K and 0.2 cm2/Vs at room temperature is obtained. We further show that the absorption edge near the pump excitation wavelength of 800 nm remains temperature independent, and is therefore not a contributing factor in our observation of larger transient signals at lower temperatures. After an initial fast decay, a power-law decay is observed in the tail of the transient response from 2 to 600 ps. The dependence of the photoconductive response on the pump fluence and the electric field amplitude of the terahertz pulse are examined. Finally, we show some preliminary results of transient photocurrent measurements on contact-biased samples using a fast oscilloscope with a system rise time of about 50 ps.

Paper Details

Date Published: 16 June 2004
PDF: 12 pages
Proc. SPIE 5352, Ultrafast Phenomena in Semiconductors and Nanostructure Materials VIII, (16 June 2004); doi: 10.1117/12.526915
Show Author Affiliations
Frank A. Hegmann, Univ. of Alberta (Canada)
Oksana Ostroverkhova, Univ. of Alberta (Canada)
Jianbo Gao, Univ. of Alberta (Canada)
Lloyd Barker, Univ. of Alberta (Canada)
Rik R. Tykwinski, Univ. of Alberta (Canada)
John E. Bullock, Univ. of Kentucky (United States)
John E. Anthony, Univ. of Kentucky (United States)

Published in SPIE Proceedings Vol. 5352:
Ultrafast Phenomena in Semiconductors and Nanostructure Materials VIII
Kong-Thon Tsen; Jin-Joo Song; Hongxing Jiang, Editor(s)

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