Defect and strain modulated highly efficient ZnO UV detector: Temperature and low-pressure dependent studies

ZnO, a wide bandgap (similar to 3.3 eV) material, can be used for ultraviolet photodetection. We have deposited ZnO thin-films on glass substrates by an automated ultrasonic spray pyrolysis system. X-ray diffraction (XRD), Raman spectroscopy suggest hexagonal wurtzite phase of prepared film and scanning electron microscope reveals its microflower like structure. The Photodetector devices have been fabricated in metal-semiconductor-metal (M - S - M) configuration. A highest responsivity of 24.38 A W-1 has been achieved at an applied bias of 5 V with the corresponding external quantum efficiency (EQE) value of 8283% for 365 nm UV irradiation. On/Off ratio of the device is similar to 454 even for a low UV intensity (1.66 mW cm(-2)) and the corresponding detectivity of the UV photodetector device is similar to 4.6 x 10(12) cm Hz(1/2) W-1. The observed high value of responsivity has been assigned to a large amount of oxygen vacancy in ZnO microflowers. Oscillation in photocurrent has been observed at low air pressure and has been assigned to a competitive dynamic process of absorption and desorption oxygen on the ZnO surface. Temperature-dependent optoelectrical properties have been analyzed based on trapping-detrapping of charge carriers in defect states and their interactions with lattice phonons.