Indium gallium zinc oxide deposited by pulsed laser deposition at room temperature was used as a channel layer to fabricate transparent thin film transistors with good electrical characteristics: field effect mobility of 11cm2V−1s−1 and subthreshold voltage swing of 0.20V∕decade. By varying the oxygen partial pressure during deposition the conductivity of the channel was controlled to give a low off-current of ∼10pA and a drain current on/off ratio of ∼5×107. Changing the channel layer thickness was a viable way to vary the threshold voltage. The effect of the gate dielectric on the electrical behavior was also explored.
A transparent memory device has been developed based on an indium gallium zinc oxide thin film transistor by incorporating platinum nanoparticles in the gate dielectric stack as the charge storage medium. The transfer characteristics of the device show a large clockwise hysteresis due to electron trapping and are attributed to the platinum nanoparticles. Effect of the gate bias stress (program voltage) magnitude, duration, and polarity on the memory window characteristics has been studied. Charge retention measurements were carried out and a loss of less than 25% of the trapped elec-trons was observed over 104 s indicating promising application as nonvolatile memory.
Europium doped gallium oxide thin film electroluminescent devices with bright, red emission (611nm) and relatively low threshold voltages of 60V were produced using pulsed laser deposition. The use of transparent conducting electrodes of amorphous InGaZnO on transparent aluminum titanium oxide/indium tin oxide/7059 Corning glass substrates resulted in a device that is transparent throughout the visible spectrum. At 100V, with 1kHz excitation, the luminance was 221cd∕m2. The Sawyer-Tower circuit analysis and time dependent emission measurements suggest that the charge trapping at the aluminum titanium oxide/Ga2O3:Eu interface plays an important role in producing efficient emission.
Europium-doped β-Ga2O3 thin films were grown on double-side polished c-axis (0001) sapphire substrates by pulsed laser deposition at 850°C. Transmission measurements of the films revealed a sharp band edge with a band gap at 5.0eV. The films exhibited intense red emission at 611nm (2.03eV) due to the transitions from D05 to F27 levels in europium, with intensities that increased with the concentration of europium. Time-resolved photoluminescence measurements revealed a temperature-insensitive lifetime of 1.4ms, which is much longer than the lifetimes of europium luminescence observed in GaN hosts.
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