Effect of Proton Irradiation Temperature on Zinc Oxide Metal-Semiconductor-Metal Ultraviolet Photodetectors

Abstract

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.