| Summary: | We have systematically studied Zinc Oxynitride (ZnON) materials for thin film transistors in advanced display applications. The
ZnON materials
were deposited
using a reactive sputtering process with a metallic Zn target in a gas mixture of
Ar, N2 and O2. We previously optimized the gas mixture and RF power
and found optimized process parameters for O2 and N2 flow rates and
RF power. In this contribution, we report the material properties as a function of process pressure and temperature. We
observed that at a relatively lower pressure of 5 mTorr, the material shows a cubic
Zn3N2-like structure with a narrow band gap of 1.1 eV, high
conductivity, high carrier density, and high carrier mobility; at medium pressure of approximately 13-15
mTorr, the material becomes nanostructured or amorphous ZnON (nc-ZnON or a-ZnON)
with a band gap of
approximately 1.3-1.5 eV; and at pressures higher than 20 mTorr, the material shows a hexagonal
polycrystalline ZnO-like structure with a band gap of 3.1 eV. The deposition rate decreases but
the band gap
increases monotonically with increasing pressure; the Hall electron mobility decreases with
increasing pressure in the range from 5 mTorr to 13 mTorr and changes very little
in the high
pressure regime; the conductivity and carrier density decrease with the
increase of pressure from 5 mTorr to 17 mTorr and then increase with further
increase of pressure, which is related to the material structure changes from
Zn3N2-like to a-ZnON, and then to ZnO-like
materials. The
substrate temperature has little effect on the material properties. Increasing substrate temperature
slightly increases the band
gap, carrier concentration, and conductivity, but slightly decreases the
carrier
mobility. Finally, under the optimized conditions, the nc-ZnON
films are made
with an optical band
gap of 1.3-1.5 eV, electron mobility above 80 cm2/Vs and
electron density
of 1 × 1018 cm-3, which are suitable for high quality TFTs in advanced display
applications.
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