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Room-Temperature-Synthesized High-Mobility Transparent Amorphous CdO–Ga2O3 Alloys with Widely Tunable Electronic Bands

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journal contribution
posted on 01.02.2018, 00:00 by Chao Ping Liu, Chun Yuen Ho, Roberto dos Reis, Yishu Foo, Peng Fei Guo, Juan Antonio Zapien, Wladek Walukiewicz, Kin Man Yu
In this work, we have synthesized Cd1–xGaxO1+δ alloy thin films at room temperature over the entire composition range by radio frequency magnetron sputtering. We found that alloy films with high Ga contents of x > 0.3 are amorphous. Amorphous Cd1–xGaxO1+δ alloys in the composition range of 0.3 < x < 0.5 exhibit a high electron mobility of 10–20 cm2 V–1 s–1 with a resistivity in the range of 10–2 to high 10–4 Ω cm range. The resistivity of the amorphous alloys can also be controlled over 5 orders of magnitude from 7 × 10–4 to 77 Ω cm by controlling the oxygen stoichiometry. Over the entire composition range, these crystalline and amorphous alloys have a large tunable intrinsic band gap range of 2.2–4.8 eV as well as a conduction band minimum range of 5.8–4.5 eV below the vacuum level. Our results suggest that amorphous Cd1–xGaxO1+δ alloy films with 0.3 < x < 0.4 have favorable optoelectronic properties as transparent conductors on flexible and/or organic substrates, whereas the band edges and electrical conductivity of films with 0.3 < x < 0.7 can be manipulated for transparent thin-film transistors as well as electron transport layers.

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