Optoelectronic characteristics of gallium oxide deep ultraviolet photodetectors with symmetric and asymmetric metal contacts

The $Ga_{2}O_{3}$ thin films were deposited on quartz substrates at different oxygen flow ratios $(O_{2}/\left[O_{2}+Ar\right]$, 0 %-5 %) by radio-frequency magnetron sputtering followed by thermal annealing at $900^{\circ}C$ for 2 h in an $N_{2}$ atmosphere. All polycrystalline $Ga_{2}O_{3}$ thin films exhibited high average transmittance above 87.8% in visible region and the 0% and 1% thin films had optical bandgap energies of about 4.9 eV. We fabricated MSM photodetectors based on the 1% $Ga_{2} O_{3}$ thin film using pairs of Ni-Ni symmetric and Ni-Al asymmetric interdigital electrodes. The Ni-Ni device had a high on/off current ratio $\left(\gt10^{5}\right)$, a responsivity of 88.7 mA/W, and a specific detectivity of $4.81 \times 10^{10} J$ at 10 V bias under UVC illumination, and the Ni-Al device exhibited self-driven behavior along with short rise and fall times (0.45 s and 0.69 s).