Impedance Spectroscopy on Poly-p-Phenylene-Vinylene Light-Emitting Diodes

Copyright © (1997) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics

We report on electrical impedance measurements on poly-p-phenylene-vinylene (PPV) light-emitting diodes in the frequency range between 100 Hz and 10 MHz. A significant difference can be revealed between the device characteristics of light-emitting diodes eliminated on indium-tin-oxide (ITO) and those of other high-work-function metals (e.g. Au). Thermal conversion of the precursor polymer on ITO substrates results in a p-type doping of the conjugated polymer PPV. Hence, devices in the configuration ITO/PPV/Al display Schottky behavior, which can be modeled by a simple equivalent circuit of two RC elements in series, representing a bulk and a junction region. The low-frequency device capacitance displays a pronounced voltage dependence and, from a detailed analysis, the ionized acceptor concentration N(A), the diffusion potential V(D), and the width of the space charge region w can be obtained. Typical values for N(A) are10**(16)-10**(17) cm**(-3), and for V(D) within the range 1-1.5 V, resulting in a width w of the space charge region at zero bias of about 50-150 nm. Via temperature-dependent investigations we reveal a transition from a p-type semiconductor Schottky diode at room temperature to a metal/insulator(polymer)/metal structure at lower temperatures.

By: M. Meier, S. Karg, W. RieB

Published in: Journal of Applied Physics, volume 82, (no 4), pages 1961-6 in 1997

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