Effects of oxygen plasma post-treatment on the structural, electrical and optical properties of Ga-doped ZnO films

Abstract

The effects of O₂ plasma post-treatment on the electrical behavior of Ga-doped ZnO (GZO) films were characterized. GZO films were spin-coated onto glass and post-treated in an O₂ plasma at a 0- to 100-W radio-frequency (RF) power and a 0- to 60-s process times in a capacitively-coupled plasma system. Atomic force microscopy, X-ray diffraction, Hall, UV-Vis spectroscopy, photoluminescence, and photocurrent measurements were used to study the influence of the O₂ plasma post-treatment on the surface morphological, electrical, and optical properties of the GZO films. With increasing RF power during the O₂ plasma post-treatment, the electrical properties of the GZO films improved significantly. The carrier concentration of the GZO films increased by a factor of approximately 52 from 5.89 × 10¹⁷ to 3.08 × 10¹⁹ cm ^-3 for a 30-s O₂ plasma exposure at 100-W RF power. The electrical improvement was attributed to the GZO films’ high crystallinity, caused by the O₂ plasma post-treatment reducing the number of oxygen defects. The plasma treatment had little effect on the transmittance of the GZO films. The optical band gap of the film increased with increasing RF power. An enhanced UV photocurrent was obtained for the GZO film after a 30-s O₂ plasma post-treatment at a 100-W RF power, and the recovery was slow.