  The electrical and structural characteristics of 50 nm zinc oxide (ZnO)
metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors subjected to
proton irradiation at different temperatures are reported and compared. We
irradiated the devices with 200 keV protons to a fluence of 1016 cm-2.
Examination of the X-ray diffraction (XRD) rocking curves indicates a strongly
preferred (100) orientation for the grains of the as-deposited film, with
decreases in crystal quality for all irradiated samples. In addition, peak
shifts in XRD and Raman spectra of the control sample relative to well-known
theoretical positions are indicative of tensile strain in the as-deposited ZnO
films. We observed shifts of these peaks towards theoretical unstrained
positions in the irradiated films relative to the as-deposited film indicate
partial relaxation of this strain. Raman spectra also indicate increases of
oxygen vacancies (V_O ) and zinc interstitials (Zn_i ) relative to the control
sample. Additionally, photocurrent versus time measurements showed up to 2x
increases in time constants for samples irradiated at lower temperatures months
after irradiation, indicating that the defects introduced by suppression of
thermally-activated dynamic annealing process has a long-term deleterious
effect on device performance.
