Solution-deposited ZnO-organic diodes with high current density and high frequency rectification under ambient condition
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1035-L05-28
Solution-deposited ZnO-organic diodes with high current density and high frequency rectification under ambient conditions Bhola N Pal, Jia Sun, Byung Jun Jung, and Howard E Katz Department of Material Science and Engineering, Johns Hopkins University, 103 Maryland Hall, 3400 N Charles Street, Baltimore, MD, 21218 ABSTRACT n-ZnO/p-Pentacene and n-ZnO/poly(bis(dodecyl)quaterthiophene) (p-PQT-12) vertical p-n junction diodes were prepared on ITO-coated glass. A continuous film of ZnO nanoparticles was grown on the ITO glass by dip-coating and subsequent heat treatment of a zinc acetate film. Pentacene was then thermally evaporated to form the ZnO/Pentacene diode, whereas PQT-12 was spin coated for the ZnO/PQT-12 diode. Based on the band energies of ZnO, pentacene and PQT-12, for efficient carrier injection, gold was chosen as the top electrode to complement the ITO for both diodes. The microstructures of ZnO and pentacene films are studied by AFM and show a layer of pentacene grains with about twice the extent of the underlying layer of ZnO grains, implying substantial interfacial contact between them The current density-voltage (J-V) measurement shows that the maximum current density for ZnO/Pentacene and ZnO/PQT12 are 160 A/cm2 and 350 A/cm2 respectively. The rectification was characterized by observation of full input-half output waves. Data indicate that these devices can operate up to frequencies of 20 MHz and 9 MHz for ZnO/Pentacene and ZnO/PQT12, respectively, under ambient environment conditions. This rectification frequency is higher than other reported organic and polymer Schottky diodes under these conditions. Turn on voltages of these diodes are also much lower than for the reported organic and polymer diodes.
Introduction: Organic semiconductors are currently the center of interest for both fundamental research and industrial application like low-cost large-area circuits [1-4] based on transistors [5-6], diodes [7-8], and memory elements [9] etc. Another enticing application is the radio frequency identification tag [1, 10-11]. High frequency RF-ID tags need a diode which can respond at 13.56 MHz frequency [12-15] with sufficient current density and have a sufficiently large reverse breakdown voltage [12-13] and a substantially lower forward turn on voltage. Operation in ambient environment is also desired for practical application. A
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semiconductor/semiconductor pn junction or a metal/semiconductor Schottky contact, as has been demonstrated in many previous publications. Currently, there have been a few reports on vertical organic Schottky diodes [16-20], although their sustained operation at >1 MHz in ambient environment necessitates encapsulation, as stated in the references and consistent with our own preliminary experiments. At the same time a large number of inorganic pn junction diodes have been reported, [21-24] although most of them have very poor current density [22-24], very low rectification ratio [22-
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