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Abstract:
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The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO)(a-ZITO) thin films and the
characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films
were very conductive and showed clear free carrier absorption FCA . The analysis of the FCA gave the effective mass value of
0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited
channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased
the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn
contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing
the Zn content, while large on–off current ratios 107–108 were kept for all the Zn contents. The field effect mobilities ranged
from 12.4 to 3.4 cm2 V−1 s−1 for the TFTs with Zn contents varying from 5 to 48 atom %. The role of Zn content is also
discussed in relation to the carrier transport properties and amorphous structures. |