Sputtering Ambient Effects on Functionality of Al-doped Gallium Oxide Films for Deep-Ultraviolet Detectors

The Al-doped gallium oxide (AGO) films were prepared on c-plane sapphire substrates at 600°C using cosputtering from Ga
2
O
3
and Al targets. An O
2
/Ar gas mixture was used during the film growth. The wide optical-bandgap and the large grain-size of annealed AGO film was found in the low oxygen mixture ratio
$(\mathrm{RO}_{2}= \mathrm{O}_{2}/[\mathrm{Ar}+ \mathrm{O}_{2}])$
. Thus, the effect of various RO
2
on optical and structural properties of AGO films and related deep-ultraviolet detector characteristics were investigated. As increasing the RO
2
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 (@900°C, 20 min), the highest optical-bandgap of 4.97 eV was achieved for the 33%- RO
2
-sputtered sample. After annealing, the AGO films with (−201) plane family were observed except the sample with 100% RO
2
. As a result, the 16%-RO
2
-annealed AGO film possesses the optimum photodetector performance, where the on/off current ratio and peak responsivity can reach
$2.00\times 105$
and 1.39 A/W (@ 5 V and 230 nm), respectively. The results indicate that the sputtering ambient trade-off is a critical issue for improving the AGO film and the photodetector performance.