Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 45: Joint Poster Session

HL 45.10: Poster

Tuesday, March 15, 2011, 18:00–21:00, P1

Optical properties of pentacene layers on zinc oxide — •Jonatan Helzel, Stephanie Jankowski, Mira El Helou, Gregor Witte, and Wolfram Heimbrodt — Philipps Universität Marburg; Department of Physics and Material Sciences Centre Germany

In comparison to other organic semiconductor pentacene has a high carrier mobility. Pentacene is one of the most promising organic semiconductors for semiconducting devices. Like many other organic semiconductors pentacene is a p-type semiconductor, hence for electronic components as e.g. diodes, an n-type semiconductor is needed. We prepared the p-pentacen films with various thicknesses on n-ZnO substrates by molecular beam deposition. Optical spectroscopy was used to study the properties of these hybrid systems. The samples have been characterized by means of absorption and photoluminescence. The HOMO-LUMO transition as well as the excitonic states have been measured in the temperature range between 10 K and room temperature. At low temperatures a thickness dependent shift was observed for the two Davydov components of the pentacene exciton. Furthermore the exciton binding energies exhibit a thickness and temperature dependence. The reason of this unique behaviour will be discussed. Pentacene and ZnO have very different thermal expansion coefficients. This leads most likely to a tensioning of the thin films and a relaxation for the upper part of the thicker films. Due to the anisotropic expansion of pentacene not only the lattice constants, but also the angle between the molecules changes, while cooling them down.