Experimental study of wide bandgap transparent conducting oxide thin films

Epitaxial growth of both pure and doped CdO thin films has been achieved on MgO (111) substrates using pulsed laser deposition (PLD). A maximum conductivity of 42,000 S/cm with mobility of 609 cm2/V· s was achieved when the CdO epitaxial film was doped with 2.5% Sn. The pure CdO epitaxial film had a bandgap of 2.4 eV. The bandgap increased with doping and reaches a maximum of 2.87 eV when the doping level was 6.2%. Both grain boundary scattering and ionized impurity scattering were found to contribute to the mobility of CdO films.; Multilayered TCO thin film structures have been designed to achieve both high conductivity and high transmittance in the visible range. The double-layered TCO structures consisted of Sri doped CdO film as conductive layer, and either Sri doped CdIn₂O₄ or Cd rich Cd₂SnO ₄ or Ga doped ZnO film as transparent layer. By optimizing the layer thickness and/or doping levels, effective conductivity of 20,600 S/cm and an average transmittance larger than 85% in the range of 400–700 nm have been achieved. These properties are attractive for future TCO applications.; Templated ZnO thin film growth from the vapor phase was achieved on docosyltrichlorosilane-patterned Si substrates using atomic layer epitaxy (ALE) combined with soft lithography. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to single-crystal Si surfaces by hot microcontact printing. Using diethylzinc and water as ALE precursors, crystalline ZnO layers were then grown selectively on the SAM-free surface regions where native hydroxyl groups nucleated growth from the vapor phase. High-resolution ZnO patterns with 1.0 μm–40 μm feature sizes were readily achieved, demonstrating that soft lithography combined with ALE is a simple and promising methodology for selective area in situ vapor phase fabrication of patterned oxide thin films.; Highly oriented Ga doped ZnO nano-rod arrays were fabricated by PLD on GaN and sapphire substrates. X-ray diffraction revealed that these nano-rods are epitaxial c-plane ZnO. The growth of the ZnO nano-rods was found to be electric-field-assisted. The morphology of the ZnO nano-rods is mainly determined by the Ga doping level and the substrate temperature. These ordered ZnO nano-rod arrays are attractive for field emission and optoelectronic applications.