Effect of Temperature and High Electric Field on the Responsivity and Speed-Performance of Gallium Oxide UV Photodetectors

Gallium oxide films were deposited by radio-frequency magnetron sputtering in an Ar/O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> atmosphere. Post-deposition annealing at 900 °C in argon for 30 minutes yielded polycrystalline β-phase Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films with high stoichiometric quality (O/Ga ≈ 1.5). The resulting films had a thickness of 390 nm and exhibited a transmittance exceeding 70% in the long-wavelength region λ ≥ 310 nm. The band gap of the film increases from 4.74 eV to 4.87 eV as the temperature decreases from 350 K to 10 K. The photoconductivity of MSM-structures at temperatures below 150 K is governed by space-charge-limited currents. Trap-filled limiting voltages of 25 V, 37 V, 49 V and 55 V were observed at 10 K, 50 K, 77 K and 100 K, respectively, corresponding to trap concentrations of 1.8×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>, 2.7×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>, 3.6×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 4.2×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>. The devices demonstrated extremely low dark currents <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> ≤ 20 pA at 500 V and a responsivity peak of 1.42 A/W at 150 K and 1100 V, indicating an internal gain mechanism. UV detectors based on Pt/β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>/Pt exhibit high-speed performance, with response and recovery times of 38 ms and 8 ms, respectively. Time-dependent photoresponse analysis revealed a decrease in rise time from 69 ms to 36 ms and in decay time from 37 ms to 10 ms as the temperature increased from 10 K to 350 K, with minimal dependence on the applied voltage.