(Invited) Effect of Temperature and 5 Mev Proton Irradiation Damage on Performance of b-Ga2O3 Photodetectors

Abstract

Effect of temperature and MeV protons at doses from 1013 -1015 cm-2 on photo-response to 254 nm wavelength, and blindness to 365 nm light, of planar photodetectors fabricated on β-Ga2O3 films grown on Al2O3 by metalorganic chemical vapor deposition. Ohmic contacts were formed by Si-implantation and annealing at 900ºC, followed by deposition of Ti/Au metallization. The photocurrent induced by 254 nm illumination increased monotonically with temperature, from ~2.5 x10-7 A at 25 ºC to ~2.2 x10-6 A at 350 ºC at a fixed 254 nm light intensity of 760 µW/cm2. The temperature dependent photo-to-dark current ratio (PDCR) for this wavelength was 328 at room temperature and decreased to ~9 at 350ºC. The responsivity increased from 5 to 36 A/W over this temperature range, with corresponding external quantum efficiencies of 2.5 x103 % at 25ºC and 1.75 x104 % at 350ºC. Similarly large numbers reported for Ga2O3 photodetectors have previously been ascribed to carrier multiplication effects. For the effect of 5 MeV protons irradiations, the photocurrent increased with dose due to the introduction of damage from non-ionizing energy loss by the protons. The total calculated vacancy concentration increased from 5x1015-5x1017 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 x10-7 A at 25 ºC for a dose of 1013 cm-2 to ~10-6 A at a dose of 1015 cm-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 1015 cm-2, with corresponding external quantum efficiencies of ~103 % in control samples, ~2 x103 % for a dose of 1013 cm-2 and 104 % for a dose of 1015 cm-2. The mechanism for the increase in photocurrent is 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.