Effects of target power and deposition pressure on magnetron-sputtered molybdenum disulfide thin films: Morphological, structural, optical, and electrical characteristics

Abstract

Radio frequency magnetron sputtering is an effective method for growing MoSS thin films with tailored optical and electrical properties for various applications. This study investigates how deposition pressure and target power impact the morphology, structural, optical, and electrical characteristics of MoSS thin films. Scanning electron microscopy (SEM) revealed a nanoflake surface morphology with flake widths from 24 to 32 nm, where lower target power produces more pronounced flake structures. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of MoO3 alongside the formation of MoS2. XPS analysis also indicated sulfur vacancies and molybdenum oxide formation due to ambient oxygen, with the Mo/S ratio significantly affected by deposition pressure at higher target powers. Optical analysis demonstrated that higher sputtering pressures enhance transparency, with transmission reaching 80 %, while lower pressures result 30 % transmission. High target power caused a red shift in the absorption edge, while reduced deposition pressure narrowed the optical band gap, ranging from 2.1 to 2.5 eV, due to defect formation and sulfur vacancies, as revealed by photoluminescence and Raman spectroscopy. Electrical measurements indicated a shift from Schottky to Ohmic contact behavior for thin films grown at lower pressures, resulting higher conductivity. Additionally, activation energy decreased with increasing target power but rose significantly with higher deposition pressures, indicating that thin films with Ohmic contact have lower activation energy than those with Schottky contact. These findings underscore the critical role of sputtering parameters, especially target power and plasma pressure, in defect engineering, which directly influences the optical and electrical performance of MoSS thin films.