Electronic Processes in Organic Electronics by Hisao Ishii Kazuhiro Kudo Takashi Nakayama & Nobuo Ueno

Author:Hisao Ishii, Kazuhiro Kudo, Takashi Nakayama & Nobuo Ueno
Language: eng
Format: epub
Publisher: Springer Japan, Tokyo

Single crystal pentacene exhibits HOMO band dispersion with a bandwidth of a few hundred meV, and its carrier mobility reaches 40 cm2/Vs [39–42]. These characteristics are produced by high coherency of the molecular lattice and a relatively large transfer integral of the π orbitals. Under this condition, both random strain in the molecular lattice and disruption of lattice coherency lead to modulation of the band structure. According to the GIXD results, the lattice coherency of the pentacene thin films on SiO2 is mainly interrupted by the small crystallite size rather than the random strain. Therefore, the mosaic structure of the polycrystalline domain with small crystallites would be the most probable cause of the band-edge fluctuation. To confirm the validity of this assumption, characteristic period of the band-edge fluctuation was also compared to the crystallite size. Inset of Fig. 10.28b shows a typical line profile of the band-edge fluctuation obtained with AFMP on a crystalline domain [7] and Fig. 10.28b shows its corresponding FFT spectrum. Although AFMP measures a completely different physical property from the topography of the substrate, the FFT spectrum has similar prominent peaks. Based on the same discussion as for Fig. 10.28a above, the highest spatial frequency of the characteristic band-edge fluctuation is concluded to be around 0.03 nm−1 (30 nm in period), which again agrees well with the crystallite size. The characteristic periods of the band-edge fluctuation are nearly constant among many pentacene films grown at different temperatures. Accordingly, it is highly probable that the mosaic structure with small crystallites causes the band-edge fluctuation.

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