Plasma-assisted electronic structure modulation of ZnO thin films for high-performance UV photodetectors

초록

The precise control of electronic structure is crucial for optimizing oxide-semiconductor ultraviolet (UV) photodetectors. In this study, the effect of Cl2 plasma treatment on ZnO thin films was systematically examined and directly correlated with the performance of ZnO-based metal-semiconductor-metal (MSM) UV photodetectors. By adjusting the bottom-bias power in an inductively coupled plasma system, both ion energy and radical flux were tuned, enabling targeted modification of the chemical composition, lattice structure, and electronic energy levels of ZnO films. X-ray photoelectron spectroscopy revealed progressive Cl incorporation and plasma-induced defect formation with increasing bottom-bias power, whereas X-ray diffraction analysis suggested lattice distortion associated with oxygen vacancies. These modifications resulted in systematic evolution of the electronic structure, including an upward shift of the Fermi level, reduction in work function, and alterations in band-edge positions. Consequently, ZnO MSM photodetectors demonstrated significant improvements in photocurrent and photoresponsivity, achieving a maximum responsivity of 374.45 mA/W under UV illumination. Although higher plasma powers resulted in increased dark current, the devices maintained stable photoconductive behavior, a wide dynamic range, and rapid response characteristics. These findings establish Cl2 plasma treatment as an effective approach for electronic structure engineering of ZnO, paving the way for the development of high-performance UV photodetectors.

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