Diode production and characterization by evaporation of silver on ZnO thin films by cold substrate method

Abstract

In this study, ZnO (Zinc Oxide) thin films, which are widely used in photoelectronic technology, were grown on glass and tin oxide-coated glass substrates by chemical spraying at a substrate temperature of 325°C. The film growth rate was set at 60 Å per minute, while the spray rate was kept at 5 ml per minute. Thus, the thickness of the obtained ZnO films was approximately 1.8-2.1μm during 30 minutes of spraying. Then, the obtained ZnO films were annealed at 350 °C, 375 °C and 400 °C for 30 minutes at room temperature. The analyses were made on four different samples. X-ray diffraction patterns showed that all samples grew in a hexagonal crystal structure. It was determined from the Scanning Electron Microscope (SEM) images that the unannealed and annealed samples at 350 °C, 375 °C and 400 °C were in the form of nanorods and underwent a structural transformation with the effect of temperature. The energy band gaps calculated from the optical transmittance spectra of the samples were found to be 3.30, 3.25, 3.06 and 3.03 eV for unannealed ZnO and annealed ZnO films at 350 °C, 375 °C, 400 °C, respectively. Defects in the crystal structure of ZnO films were determined from the photoluminescence measurements. In the second stage of the study, the samples were divided into two groups and Ag was evaporated to their surfaces at substrate temperatures of 300 K and 200 K, and Ag/ZnO/SnO₂ binary structures were obtained. For the formation of Schottky diodes, the thermal diffusion process was applied to the binary structures produced at 300 K substrate temperatures for 30 minutes at 400 °C, while the photo-stimulated diffusion process was applied to the binary structures produced at 200 K substrate temperature for 1 hour at 375 nm wavelength under Ultraviolet (UV) rays. The barrier height and reverse saturation current values of these Schottky diodes, which were created through different technological applications, were determined and the results were compared.