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Carrier transport investigation on organic semiconductor by electrical DC and AC measurements: the case of Alq3

Silva, V.M. ; Graça, M.P.F. ; Mendes, J. C. ; Costa , L. ; Pereira, L.P.

Advanced Materials Vol. 514-516, Nº --, pp. 78 - 82, May, 2006.

ISSN (print): 0935-9648
ISSN (online):

Journal Impact Factor: 8,191 (in 2008)

Digital Object Identifier: 10.4028/

In the present work, the nature of the electrical mechanism for carrier transport in Alq3 is studied by current-voltage measurements and broadband dielectric spectroscopy. The d.c. currentvoltage characteristics at low applied electrical field exhibits a classical “N” shape due to interfacial states located at metal-organic interface, but tend to disappear when successive higher forward bias is applied. Using dielectric spectroscopy it is possible to observe that the main relaxation peak shifts to a higher frequency with the increase of the applied d.c. voltage (from approximately 100 Hz with 0 V d.c. bias to approximately 400 Hz with 6 V d.c. bias) indicating a semiconductor structure change. The logarithmic Z’’ vs. Z’ plot has a slope about 0.7 that decreases to 0.5 with the increasing applied d.c. voltage, reaching a classic Debye relaxation. An attempt to correlate with some structural changes is made.