AVS 56th International Symposium & Exhibition
    Electronic Materials and Processing Wednesday Sessions
       Session EM-WeA

Paper EM-WeA1
Contact Resistance and Material Mixing at the Metal/Organic Interface

Wednesday, November 11, 2009, 2:00 pm, Room B1

Session: Contacts, Interfaces, and Defects in Semiconductors
Presenter: Y.B. Kim, Seoul National University, South Korea
Authors: Y.B. Kim, Seoul National University, South Korea
D. Jeon, Seoul National University, South Korea
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The properties of interface formed by depositing metal on an organic substrate is very different from those of an organic film deposited on a metal substrate, which is because metal atoms can easily penetrate into the loose organic substrate. The degree of mixing at the interface of metal-on-organic depends on the growth condition such as temperatrue and deposition rate. We have compared the morphology and the contact resistance of a Au electrode deposited on a pentacene film at room and liquid nitrogen temperature. The samples were prepared by thermally depositing two Au electrodes on a pentacene thin film. The resistance between the two Au electrodes was measured for different channel lengths between them so that the Au/pentacene contact resistance could be estimated by extrapolating the resistance curve to zero channel length. Figure 1 shows resistance vs channel length measured between two Au electrodes deposited at room and liquid nitrogen temperatures. For both samples, the resistance decreases with decreasing channel length. Between the two Au electrodes deposited at room and liquid nitrogen temperature, the latter yields smaller resistance and thus the smaller contact resistance when extrapolated. Atomic force microscopy revealed a much higher degree of interface mixing for Au deposited at room temperature. Interface mixing or alloying is a common method to make an Ohmic contact for the case of metal electrodes on Si. Our experiment implies that the same strategy may not be applicable to the case of metal electrodes on the organic substrates. The structural deformation of pentacene molecules seem to create traps rather than creating conductive channels. We performed Fourier transform infrared spectrascopy to check the amount of deterioration of pentacene molecules due to the Au deposition. For both liquid nitrogen temperature and room temperature deposition, the infrared peak intensity of pentacene decreased due to the Au deposition, but the peak intensity for the latter case decreased more. We will also discuss X-ray photoemission spectroscopy measurements.