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Volume: 43 | Article ID: art00009
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Effect of Metal Contact Fabrication on the Charge Injection Efficiency of Evaporated Metal Contacts on a Molecularly Doped Polymer
  DOI :  10.2352/J.ImagingSci.Technol.1999.43.3.art00009  Published OnlineMay 1999
Abstract

We previously reported that contact injection efficiencies are amenable to direct measurement in thin trap-free hole transport polymer films by a technique combining time-of-flight bulk mobility measurements with steady state current densities measured at the contact under test. In the present article, films of a trap-free molecularly doped polymer, TPD/polycarbonate, are solution coated onto a carbon-filled polymer substrate that is demonstrably ohmic for hole injection. Thermally evaporated Au and Ag as well as liquid Hg form the top contacts. Field dependent contact injection efficiencies are computed from the combined measurements and monitored over time. A persistent pattern in the evolution of contact injection efficiency with time is revealed. Invariably contact injection efficiencies evolve by orders of magnitude from initially blocking to ohmic or to an equilibrium value dependent on the nature of the metal. For thermally evaporated Au contacts, coating studies suggest that the slow stage in the observed two-stage evolution of contact formation represents a process of recovery from damage to the transport layer's surface caused by the accumulating hot Au atoms. Such a process is not observed for substrate Au. Comparisons of the evolution in injection efficiencies of evaporated Ag contacts with substrate Ag, as well as of liquid Hg contacts, demonstrate that the initially blocking nature of the contact and a fast evolution process are not associated with recovery of the interface from thermal damage but are probably a more general aspect of contact formation.

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A. Ioannidis, J. S. Facci, M. A. Abkowitz, "Effect of Metal Contact Fabrication on the Charge Injection Efficiency of Evaporated Metal Contacts on a Molecularly Doped Polymerin Journal of Imaging Science and Technology,  1999,  pp 242 - 247,  https://doi.org/10.2352/J.ImagingSci.Technol.1999.43.3.art00009

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Copyright © Society for Imaging Science and Technology 1999
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