Abstract
We unveiled the effect of doping on the morpho-structural and opto/electrical properties of Ca-doped ZnO:Al thin films obtained by RF magnetron sputtering. Scanning electron microscopy (SEM) was performed to reveal the surface morphology, while the composition and crystal structure were investigated by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The correlation between the microstructure and the electrical conductivity identifies an increase in electrical conductivity up to 145 × 10−3 Ω−1·m−1 at 5 wt.% Ca doping level with the decrease in the grain size. Furthermore, the presence of Ca dopant triggers the occurrence of the emission peak at 430 nm and an increase of the green emission peak in PL spectra. Corroborating the electrical measurements with X-ray diffraction and optical measurements, one can infer that the electrical conductivity is dominated by intrinsic defects developed during deposition and by the existence of dopants.
Highlights
Zinc oxide (ZnO) thin films prepared by physical methods such as radio frequency magnetron sputtering continue to be of high interest due to their low cost and low absorption of visible light, triggering an enhanced UV photoresponse of the photodetector, transparent conductive electrodes in solar cells, and fluorescence imaging performance [1,2,3].In addition to good absorptivity, high conductivity is the prerequisite for their applications in electro-optic devices
Corroborating the electrical measurements with X-ray diffraction and optical measurements, one can infer that the electrical conductivity is dominated by intrinsic defects developed during deposition and by the existence of dopants
Wang et al [12] investigated Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering, when the co-doping induces a significant decrease of the film resistivity in comparison with either Al or F doping, revealing the effectiveness of Al and F co-doping on electrical properties of ZnO thin films
Summary
Zinc oxide (ZnO) thin films prepared by physical methods such as radio frequency magnetron sputtering continue to be of high interest due to their low cost and low absorption of visible light, triggering an enhanced UV photoresponse of the photodetector, transparent conductive electrodes in solar cells, and fluorescence imaging performance [1,2,3].In addition to good absorptivity, high conductivity is the prerequisite for their applications in electro-optic devices. Wang et al [12] investigated Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering, when the co-doping induces a significant decrease of the film resistivity in comparison with either Al or F doping, revealing the effectiveness of Al and F co-doping on electrical properties of ZnO thin films. Besides these intensively investigated ZnO-based alloys, II–VI compounds with a rock salt structure and a band-gap above 7 eV (7.2 eV in the case of calcium oxide and 7.8 in the case of MgO) are known for enhancing the transmittance of the ZnO film [13]. An efficient transparent conductive gas diffusion barrier, with improved optical, electrical, and moisture/oxygen barrier properties, was developed when periodical dopant layers (Mg- and Al-) were inserted in the ZnO film [14]
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