| The primary aim of the present work is to gain a better understanding of the fundamentals and factors affecting the properties of alternative transparent conducting oxides (TCOs) in order to grow films with controlled properties. The two systems studied here as substitutes for indium tin oxide (ITO) are molybdenum oxide and gallium doped ZnO. The two systems not only offer commercial benefits but also some key technical advantages compared to ITO. To investigate the fundamentals properties, the novel TCO films have been grown on various substrates (sapphire, glass and polymer) and under different deposition conditions using pulsed laser deposition (PLD) technique. Film have been characterized in detail using combination of tools (XRD, TEM, XPS, 4-probe resistivity measurements, Hall measurements and absorption/transmission spectroscopy) in order to establish processing---structure---property relationship.; A novel class of TCOs based on MoOx films is proposed for development, where the electrical and optical properties can be controlled by controlling the fraction of molybdenum ions in different oxidation states (Mo4+, Mo5+ and Mo6+). The structural characterization confirmed the epitaxial growth of monoclinic MoOx films on (0001) sapphire (corundum structure) substrates, which is explained via domain matching epitaxy (DME). MoOx films annealed in air at 250°C for 1h possessed an optimal combination of high transmittance (~65%) and electrical resistivity (in the range of 1 x 10-3 O-cm) and the relative concentration of Mo4+, Mo5+ and Mo6+ states is determined to be 17.2%, 8.4% and 74%, respectively. In case of doped ZnO, the effect of Ga on the electrical and optical properties of ZnO films has been studied systematically as a function of Ga concentration. A 5%Ga:ZnO film deposited at 400°C and 2x10-2 torr of oxygen exhibited %T > 80% and a room temperature value of resistivity ~1.4x10 -4 O-cm. A VOC = 0.5 V and power efficiency of 1.25+/-0.05% achieved for non-optimized device structures with ZnGaO anodes suggests that these TCO materials can provide potential substitutes for ITO. |
