Dresden 2003 – scientific programme

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HL: Halbleiterphysik

HL 25: Organische Halbleiter II

HL 25.3: Talk

Tuesday, March 25, 2003, 15:45–16:00, BEY/81

Hysteresis of Current-Voltage Characteristics of CuPc thin film based diodes — •G. Pham, T.U. Kampen, I. Thurzo, and D.R.T. Zahn — Institut für Physik, Technische Universität Chemnitz, D-09107 Chemnitz

Current-voltage (IV) and capacitance-voltage (CV) characteristics of CuPc thin films on ITO with Ag contacts deposited in UHV were measured in situ. A current hysteresis was found between up and down bias sweep directions, which is gradually reduced when a longer delay time between successive current readings is chosen. Several mechanisms responsible for the current hysteresis are considered. Reverse bias leads to an extremely low steady-state current indicating a poor injection of holes from Ag into CuPc. Using the thermionic emission model for the reverse current, a barrier height of (0.9± 0.01) eV was found for the CuPc/Ag interface. The forward current, on the other hand, increases first by many orders of magnitude in a narrow voltage range, then increases with a reduced slope. This behaviour can be understood in terms of carrier injection from ITO into CuPc layers followed by space charge limited conduction with an exponential distribution of traps in the organic layer. Further evidence for the two distinct mechanisms was found after analysing the forward current as a function of organic layer thickness. Presence of band bending may be possible since the serial equivalent capacitance increases with increasing forward bias like in doped semiconductors.