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

doi:10.1117/12.526915

16 June 2004 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

Proceedings Volume 5352, Ultrafast Phenomena in Semiconductors and Nanostructure Materials VIII; (2004) https://doi.org/10.1117/12.526915
Event: Integrated Optoelectronic Devices 2004, 2004, San Jose, CA, United States

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.

Citation Download Citation

Frank A. Hegmann, Oksana Ostroverkhova, Jianbo Gao, Lloyd Barker, Rik R. Tykwinski, John E. Bullock, and John E. Anthony "Picosecond transient photoconductivity in organic molecular crystals", Proc. SPIE 5352, Ultrafast Phenomena in Semiconductors and Nanostructure Materials VIII, (16 June 2004); https://doi.org/10.1117/12.526915

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