Abstract
Transparent conducting films of zinc oxide and indium-doped zinc oxide have been prepared by a simple and economical sol-gel technique. This process is feasible for the fabrication of high quality TCO thin films when the processing parameters are optimized. It was found that the out-diffusion of oxygen during the vacuum annealing step was a crucial factor to prepare thin layer with superior properties. Annealing lowers the resistivity down to 4.7 10-3 Ω·cm for the 1 at.% doped films due to the liberation of high-valency In-dopants and the enhanced film density. At high indium concentrations, the free electron density stabilizes because an increasing number of dopant atoms form some kinds of neutral defects. The neutralized indium atoms do not contribute free electrons. The feasibility to deposit highly transparent ZnO thin films has been demonstrated.
Highlights
Zinc oxide thin films have been actively investigated as transparent conducting oxide (TCO) to substitute indium tin oxide (ITO) due to price volatility associated with indium, along with various supply concerns
Zinc oxide is relatively stable in the presence of hydrogen plasma, which is of significance for applications related to amorphous silicon solar cells
One should note that the TG/differential thermal analysis (DTA) results should not be directly extrapolated to the case of a film, because they were recorded on gel powders and at a slow heating rate, whereas the films prepared in this study were rapidly calcined in a preheated furnace [26]
Summary
Zinc oxide thin films have been actively investigated as transparent conducting oxide (TCO) to substitute indium tin oxide (ITO) due to price volatility associated with indium, along with various supply concerns. The values reported for the electrical resistivities are relatively divergent and have not changed significantly, despite the large number of groups working in the field of TCO materials This suggests that a physical limitation probably exists which prevents reaching resistivities lower than 1 × 10−4 Ω∙cm and mobilities larger than about 40 cm2/V∙s. The suitable manipulation of precursor solutions allows for the fabrication of advanced materials in a wide variety of forms including thin film coatings and very homogeneous powders Despite all these advantages, very few reports [21] [22] are published on solgel processed IZO thin films. The elero-optical properties of IZO films are interpreted taking into account the intrinsic characteristics of sol-gel technique, which is very different from the other physical and chemical methods
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