Influence of oxygen on sputtering of aluminum-gallium oxide films for deep-ultraviolet detector applications

Abstract

The aluminum-gallium oxide (AGO) films were prepared on c-plane sapphire substrates at a substrate temperature of 600 °C using co-sputtering from the Ga2O3 and Al targets. The Ar and O2 mixed gas was used during the film growth. The wide optical-bandgap and the large grain-size of annealed AGO film was found in the low O2 concentration (CO2 = [O2]/[O2+Ar] × 100%). Thus, the effect of various CO2 on optical and structural properties of AGO films and related deep-ultraviolet photodetector (DUV PD) characteristics were investigated. All AGO films possessed superior transmittance above 82% in the visible region. As increasing the CO2 from 0 to 100%, the optical bandgaps of the as-deposited AGO films increased gradually from 4.56 to 5.04 eV. After post-thermal annealing in the air at 900 °C for 20 min, the highest optical-bandgap of 4.97 eV was achieved for the 33%-CO2-sputtered sample. It was found that the as-deposited AGO films showed the amorphous network. After annealing, the AGO films with (−201) plane family were observed except the sample with 100% CO2. As a result, the 16%-CO2-annealed AGO film possesses the optimum DUV PD performance, where the on/off current ratio and peak responsivity can reach 2.00 × 105 and 1.39 A/W (at 5 V and 230 nm), respectively. The results indicate that the trade-off of CO2 sputtering ambient has played an important role in determining the annealed AGO film as well as the DUV PD properties.