Transmission and Reflection Spectra of Zinc Oxide Implanted with a High Dose of Cobalt Ions

Optical transmission and reflection spectra of monocrystalline zinc oxide (ZnO) plates implanted with 40 keV Co+ ions to high doses of (0.5–1.5)·1017 cm–2 are presented. With increasing dose, the transmission value decreases and the optical transmission edge shifts towards the long-wavelength region in transmission spectra. Also, in the transmission spectra, three absorption bands are observed in the range of 550–680 nm. The bands and their positions are typical of optically active Co2+ ions in the zinc cation substitution positions in the ZnO matrix. The reflection coefficient of the implanted side of the ZnO plate increases monotonically with increasing dose values. In both the initial and implanted ZnO plates, when reflection spectra are recorded from the reverse (nonirradiated) side, a characteristic structure at l = 375 nm is observed due to exciton reflection. Modeling of light transmission and reflection in cobalt-implanted ZnO samples was carried out within the framework of a three-layer model, in which the first surface layer contains cobalt nanoinclusions, the second, deeper layer is a solid solution of cobalt ion substitution in the ZnO matrix, the third layer is the unirradiated part of the ZnO plate. Modeling was used to determine effective refractive indices of two ZnO layers containing implanted cobalt admixture in different phase states.