Organic/inorganic heterojunction based on conducting polymer and pulse-laser-deposited (PLD) ZnO
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Organic/inorganic heterojunction based on conducting polymer and pulse-laser-deposited (PLD) ZnO Weining Wang, Leandro Gutierrez, Arya Nabizadeh, and Mehmet A. Sahiner Department of Physics, Seton Hall University, 400 South Orange Ave. South Orange, NJ 07079, U.S.A. ABSTRACT Organic/inorganic heterojunctions have been fabricated by spin coating p-type poly (3, 4 ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) onto n-type zinc oxide (ZnO) films. The ZnO films were deposited onto indium tin oxide (ITO) coated glass by pulse laser deposition (PLD) technique. The current density-voltage (J-V) characteristics of the PLDZnO/PEDOT:PSS junction based on as-deposited PLD-ZnO film shows a good rectifying behavior with a rectification ratio of 156 at ±1 V, indicating the formation of a diode between ZnO and PEDOT:PSS. Using thermionic emission model, the ideality factor (n=2.1) and barrier height (0.66 eV) of the heterojunction were obtained. Those diode parameters are better than those of the chemical vapor deposited ZnO/PEDOT:PSS heterojunction reported elsewhere, indicating that PLD may be a promising technique on fabricating high quality ZnO/polymer heterojunctions. INTRODUCTION ZnO/polymer heterojunction has attracted a considerable interest for its potential application in solar cell, LED, UV photodetection and other applications [1-5]. To fabricate high performance devices, high quality Schottky junction need to be formed at the ZnO/polymer junction. Recently, Nakano et al. [6] showed that high quality ZnO/ heterojunction can be fabricated based on bulk ZnO single crystal. Sharma, et. al [7] showed that a p-n junction can be achieved using ZnO/PEDOT:PSS heterojunction based on chemical vapor deposited ZnO film. However, there are few studies [8] on ZnO/polymer heterojunction based on pulsed laser deposited (PLD)-ZnO films. Comparing with other methods, PLD has the advantage of congruent evaporation, and being able to grow high quality thin films at relatively low temperature. It has been shown that high quality of ZnO films can be fabricated on Indium Tin Oxide (ITO) using PLD technique [9]. In this work, we report our studies on the fabrication and characterization of ITO/ZnO/PEDOT:PSS heterojunctions using PLD technique. The effect of vacuum annealing of PLD-ZnO film on the heterojunctions will also be discussed. EXPERIMENTAL DETAILS ZnO films were prepared on ITO coated glass substrates using pulse-laser deposition. Before deposition, the ITO substrates were cleaned in an ultrasonic bath using acetone, deionized water and isopropanol. After cleaning of ITO, ZnO layer was deposited on ITO by pulsed laser deposition using a KrF excimer laser with a wavelength of 248 nm. The laser pulse energy was set to 100 mJ and
the laser pulse frequency was held at 10 Hz. The distance between the ITO substrate and the ZnO target was set to 6 cm. The base pressure of the deposition system was 6.7 × 10-4 Pa (5 × 106 Torr). The substrate temperature was held at 300 ºC during deposition, on a rotating stage to improve uni
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