Abstract
In this work, we have investigated the effects of ytterbium (Yb) doping concentration on the structure and near band-edge (NBE) photoluminescence (PL) of ZnO thin films on Si after high temperature annealing. The films were made by magnetron sputtering in an Ar:O2 atmosphere. The structure of the films have been studied by Rutherford backscattering spectrometry, X-ray diffraction (XRD), scanning electron microscopy, and X-ray photoelectron spectroscopy. XRD indicates that the crystallinity of the ZnO improves with annealing temperature in the range 700–1000 °C; and after the 1000 °C annealing, the crystallinity of the films show overall an improvement for increasing Yb concentration up to 1.35 at.%. At the higher temperatures the films react with Si substrate to form silicates with Zn and Yb, and the Yb has redistributed in the film and piles up towards the Si substrate. The PL measurements show that the NBE PL intensity of the films is correlated with the crystallinity for variations in annealing temperature and Yb concentration. The PL excitation measurements suggest that the films prepared with Yb addition have higher NBE PL efficiency than the un-doped ZnO, while the energy transfer between the host ZnO and Yb ions are not efficient.
Highlights
The II-VI metal oxide semiconductor zinc oxide (ZnO), has a band gap of 3.37 eV and an exciton binding energy of 60 meV at room tem perature, which makes it a promising material for ultraviolet photonic applications [1,2,3,4,5]
Guillaume et al [23] recently reported that there was a decrease in the near band-edge (NBE) PL in their ZnO films containing low concentrations (0.3 at.%) of Yb, while Kabongo et al [24] observed a significant increase of UV emission from Yb doped ZnO nano-phosphors with Yb concentration of 0.5 mol% and an obvious decrease with the Yb concentration up to 0.75 mol%
We study ZnO films doped with different Yb concen trations, and focus on the effects on the structure and NBE PL of the films after high temperature annealing
Summary
The II-VI metal oxide semiconductor zinc oxide (ZnO), has a band gap of 3.37 eV and an exciton binding energy of 60 meV at room tem perature, which makes it a promising material for ultraviolet photonic applications [1,2,3,4,5]. A typical photoluminescence (PL) spectrum of ZnO consists of an ultraviolet (UV) emission band corresponding to near band-edge (NBE) emission and a broad defects-related band [6,7,8,9] in the visible (VIS). Both bands are strongly dependent on the preparation-, doping- and annealing-conditions of the ZnO. We study ZnO films doped with different Yb concen trations, and focus on the effects on the structure and NBE PL of the films after high temperature annealing.
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