INVESTIGATING THE INFLUENCE OF SILVER DOPING ON ZINC OXIDE THIN FILMS FOR HIGH-CAPACITANCE SUPERCAPACITOR ELECTRODES

Abstract

Zinc oxide (ZnO) has garnered significant attention as a II-VI semiconductor with a direct band gap of approximately 3.2 eV, making it suitable for near ultraviolet applications. This compound exhibits unique properties, such as an exciton binding energy of about 60 meV, making it appealing for optoelectronic devices. The natural n-type behavior of ZnO can be attributed to its deviation from stoichiometry, leading to the presence of interstitial Zn atoms (Zni) and oxygen vacancies (Vo) within the crystal lattice. Background donors like hydrogen (H) and aluminum (Al) also contribute to its n-type characteristics by forming donor levels around 0.05 eV.

In this study, we explore the wurtzite crystal structure of ZnO, where oxygen atoms are arranged in a hexagonal close-packed lattice, and zinc atoms occupy half the tetrahedral sites. The relative openness of the ZnO structure, with empty octahedral sites and half the tetrahedral sites, allows for the incorporation of external dopants, enhancing its applicability for diverse technological advancements.

During the 1950s, Zinc oxide experienced intensive research focusing on topics such as bulk and surface polarons, luminescence, and lasing. However, this interest waned in the following decades, mainly due to the challenges in achieving p-type doping in ZnO. As research interests shifted towards reduced dimensionality structures, such as the GaAs/Al1-yGayAs system, ZnO took a backseat in the scientific community.

In recent years, there has been a resurgence of interest in ZnO due to its potential in various applications, including optoelectronics, sensors, and transparent electronics. This renewed interest stems from advancements in doping techniques and a deeper understanding of its defect-related properties. This review explores the current state of research on ZnO, focusing on the latest advancements in material synthesis, doping strategies, defect engineering, and emerging applications. We discuss the challenges faced in achieving p-type doping and the innovative approaches proposed to overcome these limitations. Additionally, the promising developments in reduced dimensionality structures, such as ZnO nanowires and thin films, are presented, showcasing their potential for future electronic and optoelectronic devices.