Effect of 5 MeV proton irradiation damage on performance of β-Ga₂O₃ photodetectors

Planar thin film β-Ga₂O₃ photodetectors were irradiated with 5 MeV protons at doses from 10¹³ to 10¹⁵cm^-2, and the resulting effects on photocurrent, responsivity, quantum efficiency, and photo-to-dark current ratio at 254 nm wavelength were measured at both 25 and 150 °C. The photocurrent increased with dose due to the introduction of damage from nonionizing energy loss by the protons. The total calculated vacancy concentration increased from 5 × 10¹⁵ to 5 × 10¹⁷ cm^-3 over the dose range investigated. The dark current increased in proportion with the implant dose, leading to a decrease in the ratio of photocurrent to dark current. The photocurrent induced by 254 nm illumination increased with dose, from ∼0.3 × 10^-7 A at 25 °C for a dose of 10¹³cm^-2 to ∼10^-6 A at a dose of 10¹⁵cm^-2 at a fixed light intensity of 760 μW/cm². The photo-to-dark current ratio decreased from ∼60 in the control samples to ∼9 after proton doses of 10¹⁵cm^-2, with corresponding external quantum efficiencies of ∼10³% in control samples, ∼2 × 10³% for a dose of 10¹³cm^-2, and 10⁴% for a dose of 10¹⁵cm^-2. The mechanism for the increase in photocurrent is the introduction of gap states, since the dark current of the photodetectors was increased by illuminating with sub-bandgap (red or green laser light) for the proton irradiated samples.