Picosecond transient photoconductivity in organic molecular crystals

Frank A. Hegmann, Oksana Ostroverkhova, Jianbo Gao, Lloyd Barker, Rik R. Tykwinski, John E. Bullock, John E. Anthony

Research output: Contribution to journalConference articlepeer-review

8 Scopus citations


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 cm 2/Vs at 10 K and 0.2 cm 2/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.

Original languageEnglish
Pages (from-to)196-207
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 2004
EventUltrafast Phenomena in Semiconductors and Nanostructure Materials VIII - San Jose, CA, United States
Duration: Jan 26 2004Jan 29 2004


  • Carrier dynamics
  • Mobility
  • Organic molecular crsytals
  • Organic semiconductors
  • Pentacene
  • Primary photoexcitations
  • Terahertz pulses
  • Transient photoconductivity
  • Ultrafast

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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