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

Tuesday, 30 May 2017: 11:40
Cambridge (Hilton New Orleans Riverside)
F. Ren, S. J. Pearton, S. Ahn (University of Florida), J. Kim, Y. Jung, S. Oh (Korea University), M. A. Mastro, J. K. Hite, and C. R. Eddy Jr. (U.S. Naval Research Laboratory)
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.