Effect Of Zinc Oxide RF Sputtering Pressure on the Structural and Optical Properties of ZnO/PEDOT:PSS Inorganic/Organic Heterojunction

Zinc oxide nanostructures are deposited on glass substrates in the presence of oxygen reactive gas at room temperature using the radio frequency magnetron sputtering technique. In this research, the effects of zinc oxide sputtering pressure on the nanostructure properties of the deposited layer are investigated. The deposition pressure varies from 7.5 to 20.5 mTorr. AFM results show that with an increase in the deposition pressure, the grain size increases and the surface roughness decreases. The energy gap measured for the zinc oxide layers deposited at the pressures of 7.5, 14 and 20.5 mTorr was 3.26, 3.18, and 3.19 eV, respectively. In order to investigate the junction between zinc oxide and poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), a polymeric layer of thickness of 50 nm is deposited on a 300 nm zinc oxide layer by spin coating technique. The dark I-V characteristics indicate that the reverse saturation current density is 1.82* 10^(-6), 1.96 *10^(-7) and 7.58* 10^(-8) A/cm^(2) for the deposition pressures of 7.5, 14, and 20.5 mTorr, respectively. By increasing the deposition pressure the ideality factor of the resulting Schottky barrier dropped from 3.4 to 1.7. The effective Schottky barrier height of 0.73, 0.78, and 0.81 eV was obtained for the same order of deposition pressures. It was found that the highest optical response could be obtained for the samples deposited at the deposition pressure of 14 mTorr.