Impact of electron cyclotron wave resonance plasma on defect reduction in ZnO thin films

This study presents the fabrication of highly photosensitive undoped zinc oxide (ZnO) thin films for vacuum ultraviolet (VUV) radiation detection, covering the wavelength range of 100-200 nm. ZnO films were deposited using hybrid pulsed reactive magnetron sputtering, assisted by ECWR (electron cyclotron wave resonance) plasma. Control of the ECWR power (P_ECWR), ranging from 0 to 380 W, played a crucial role in enhancing the films' photoconductive properties. At P_ECWR = 200 W, the photosensitivity increased by 8 orders of magnitude compared to films deposited without ECWR assistance. This improvement was attributed to a sharp reduction in dark current due to lower defect density. Photoluminescence and cathodoluminescence spectra revealed a significant reduction in defect-related emissions for films deposited at P_ECWR = 200 W, confirming fewer intrinsic defects. Raman spectroscopy also showed a decrease in defect-related vibrational modes in the same films. Time-Resolved Microwave Conductivity (TRMC) measurements further supported these findings, demonstrating rapid recombination of charge carriers at 200 W, indicative of low trap densities. These results suggest that precise control of ECWR power allows for optimization of the defect concentration and crystallinity in ZnO films, paving the way for the development of high-sensitivity VUV photodetectors.