Heterojunction bipolar assembly with CrxTi1-xO2 thin films and vertically aligned ZnO nanorods

Polycrystalline and homogeneous CrxTi1-xO2 thin films were deposited on silicon (Si) substrates and on indium doped tin oxide (ITO) coated glass substrates by spin coating technique. We report the p-type conductivity in CrxTi1-xO2 thin films (x = 0.005, 0.05, 0.1, 0.15, 0.2) and variable turn-on voltages (V-O) in heterojunction ZnO-nanorod/CrxTi1-xO2/ITO bipolar device. Results showed that V-O varies substantially from similar to 0.8 V (x = 0.005) to similar to 0.53 (x = 0.2) for the bipolar assembly. X-ray photoelectron spectroscopy (XPS) showed that chemical state of Ti is the +4 valence state and Cr remains in three different oxidation states of +3. XPS in the valence band region showed a shift in the binding energy towards the lower energy side with increasing Cr intake confirming more p-type conductivity in CrxTi1-xO2 thin films. (C) 2010 Elsevier B.V. All rights reserved.