In this paper, we present the current research efforts on the atomic layer deposition (ALD) ZnO based TFT
devices carried out in our laboratory. ZnO thin film deposition was carried out by two different ALD processes; thermal
ALD using water as a reactant and plasma-enhanced ALD using oxygen plasma as a reactant. The film properties were
comparatively studied showing large difference in terms of electrical properties. For thermal ALD ZnO, carrier
concentrations were too high to fabricate well-operated ZnO TFTs. To control the carrier concentration, nitrogen doping
was utilized based on NH4OH reactant. Meanwhile, for PE-ALD, highly resistive films were obtained at low growth
temperature below 200 °C. To reduce the resistivity to a proper level for the fabrication of TFTs, UV-light exposure was
used. At properly controlled conditions, high performance TFT devices were fabricated based on these processes. ZnO
TFTs were also fabricated on flexible substrates and the initial research was carried out on the effects of device bending
on device properties.
KEYWORDS: Zinc oxide, Aluminum, Solar cells, Transparent conductors, Doping, Air contamination, Oxides, Thin film solar cells, Thin films, Metalorganic chemical vapor deposition
Transparent conductive oxides have an important role of thin-film solar cell to the side of cost and performance.
Especially, an Al doped ZnO film is a very promising material for thin-film solar cell fabrication because of the easy
synthesis method as well as the cheap cost induced on the wide availability of its constituent raw materials. The Al-doped
ZnO films were prepared by metal organic chemical vapor deposition using a diethylzinc, water vapor and
trimethylaluminum (TMA). The introduction of TMA doping source has a great influence on the electrical resistivity and
diffused light to wide wavelength range. The haze factor of Al doped ZnO achieved 43 % at 600 nm without additional
surface texturing process by simple TMA doping. In this study, the choice of AZO TCO allows the achievement of
energy conversion efficiencies to 7.7 %.
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