Microstructural and optoelectronic properties of sputtered Al:ZnO films and Al:ZnO/Cu bilayer structures: Effects of substrate and Cu thickness.

• Results show that higher crystal quality is obtained using quartz substrate. • Emission properties are strongly affected by substrate and Cu thickness. • Resistivity and mobility of Al:ZnO /Cu decreases with increasing of Cu thickness. • The bilayer/glass substrate with a thickness of 13 nm Cu has the best figure of merit. In this study, using a multi-source confocal radio frequency magnetron sputtering system, we synthesized aluminum doped zinc oxide (AZO) single layers and AZO/Cu bilayers on glass and crystalline quartz substrates with a constant AZO thickness of 65 nm and variable Cu bottom layers with a thickness of 4–13 nm. The microstructural, morphological, optical, and electrical characteristics of all samples were investigated using a variety of spectroscopic techniques. The X-ray diffraction results show that all films prepared on both substrates have a hexagonal wurtzite crystal structure and exhibit the preferred orientation along the (002) plane with some microstructural variations. The atomic force microscopy images revealed that the thickness of the Cu layer and substrate type greatly affect the films' topography and surface roughness. The transmittance spectra indicate that the single AZO layer on both substrates possess the highest average visible transmission; however, all the samples deposited on glass substrates show greater transmittance than that on quartz. Photoluminescence analysis put into evidence a decrease in ultraviolet emission with Cu thickness for both substrates, with intensities varying according to substrate type. Hall Effect measurements reveal that all samples have n-type conductivity as well as that Cu thickness has a significant impact on their electrical characteristics. Moreover, a higher value of the figure of merit is achieved with the AZO/Cu bilayer structure grown on a glass substrate with 13 nm of Cu layer thickness. [ABSTRACT FROM AUTHOR]