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Determination of Traps in Poly(p-phenylene vinylene) Light Emitting Diodes by Chargebased Deep Level Transient Spectroscopy

Published online by Cambridge University Press:  01 February 2011

Olivier Gaudin
Affiliation:
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
Richard B. Jackman
Affiliation:
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
Thien-Phap Nguyen
Affiliation:
Laboratoire de Physique Cristalline, Institut des Matériaux Jean Rouxel, Université de Nantes, 2 rue de la Houssinière, 44 322 Nantes Cedex 03, France
Philippe Le Rendu
Affiliation:
Laboratoire de Physique Cristalline, Institut des Matériaux Jean Rouxel, Université de Nantes, 2 rue de la Houssinière, 44 322 Nantes Cedex 03, France
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Abstract

Charge-based deep level transient spectroscopy (Q-DLTS) has been used to study the defect states that exist within poly(p-phenylene vinylene) (PPV), a semiconducting polymer with a band gap of about 2.4 eV. The technique allows the determination of activation energies, capture cross-sections and trap concentrations. In some circumstances, it is also possible to distinguish between minority and majority carrier traps. The structures investigated here consisted of ITO/PPV/MgAg light emitting diode (LED) devices. Two types of trapping centres were found. The first type has activation energies in the range 0.49 – 0.53 eV and capture cross-sections of the order of 10-16 – 10-18 cm2. It shows a Poole-Frenkel, field assisted-emission process. This level has been identified as a bulk acceptor-like majority carrier (i.e., hole) trap. The second type has activation energies in the range 0.40 – 0.42 eV and capture cross-sections of the order of 10-19 cm2. This level has been identified as a minority carrier (i.e., electron) trap. This second trap type is therefore expected to limit minority carrier injection into the PPV layer within the LED, and hence reduce electroluminescence under forward bias conditions.

Type
Research Article
Copyright
Copyright © Materials Research Society 2002

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