Room-Temperature-Synthesized High-Mobility Transparent Amorphous CdO-GaO Alloys with Widely Tunable Electronic Bands.

In this work, we have synthesized CdGaO 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 CdGaO alloys in the composition range of 0.3 < x < 0.5 exhibit a high electron mobility of 10-20 cm V s with a resistivity in the range of 10 to high 10 Ω cm range. The resistivity of the amorphous alloys can also be controlled over 5 orders of magnitude from 7 × 10 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 CdGaO 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.