Amorphous CdO-In2O3 alloy thin films with high conductivity and transparency synthesized by sol-gel method

Abstract

The growth of CdO-In2O3 amorphous oxide semiconductor alloys with high mobility in a wide composition range, suitable for many optoelectronic applications, has been previously reported using room temperature sputtering. In the present work, we synthesized Cd1−xInxO1+δ alloy thin films across the entire composition range using the non-vacuum, low-cost sol-gel spin coating method. Structural, electrical and optical properties of these alloy films were studied using a variety of analytical tools. We find that the alloy films become amorphous within the In composition range of 0.2 <x < 0.7, while films with x < 0.2 and x > 0.7 have the rocksalt CdO and bixbyite In2O3 structure, respectively. As-grown amorphous alloys have resistivity in the ranging from high 10−3 to low 10−2 Ω-cm due to their relatively low mobility of<10 cm2/Vs. Electrical properties of these amorphous films are improved after annealing at ~400 °C with a mobility of ~10 cm2/Vs and a low resistivity in the low 10−3 Ω-cm range. The optical gap varies from 2.54 to 3.52 eV with increasing In mole fraction, so that transmittance> 85% over a wide transmission window of ~400–1600 nm can be achieved. The low temperature, low-cost non-vacuum processing, wide bandgap tunability, and low resistivity, make these sol-gel alloy films promising materials for optoelectronic applications, especially on organic layers and/or flexible substrates.