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 presenceof oxygen reactive gas at room temperature using the radio frequency magnetronsputtering technique. In this research, the effects of zinc oxide sputtering pressure on thenanostructure properties of the deposited layer are investigated. The deposition pressurevaries from 7.5 to 20.5 mTorr. AFM results show that with an increase in the depositionpressure, the grain size increases and the surface roughness decreases. The energy gapmeasured for the zinc oxide layers deposited at the pressures of 7.5, 14 and 20.5 mTorrwas 3.26, 3.18, and 3.19 eV, respectively. In order to investigate the junction betweenzinc 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 byspin coating technique. The dark I-V characteristics indicate that the reverse saturationcurrent density is 1.82 10-6, 1.96 10-7 and 7.58 10-8 A/cm2 for the depositionpressures of 7.5, 14, and 20.5 mTorr, respectively. By increasing the deposition pressurethe ideality factor of the resulting Schottky barrier dropped from 3.4 to 1.7. Theeffective Schottky barrier height of 0.73, 0.78, and 0.81 eV was obtained for the sameorder of deposition pressures. It was found that the highest optical response could beobtained for the samples deposited at the deposition pressure of 14 mTorr..