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

TL;DR

This study investigates how proton irradiation at different temperatures affects the structural and electrical properties of ZnO UV photodetectors, revealing long-term performance degradation due to defect formation and strain relaxation.

Contribution

It provides new insights into the effects of irradiation temperature on defect dynamics and strain in ZnO UV photodetectors, which was not previously well understood.

Findings

Irradiation causes decreased crystal quality and strain relaxation in ZnO films.

Oxygen vacancies and zinc interstitials increase after irradiation.

Lower temperature irradiation leads to longer-lasting performance degradation.

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.