Effects of MgO-Buffer Layer on the Structural and Optical Properties of Polycrystalline ZnO Films Grown on Glass Substrate

Abstract

Characteristics of ZnO films grown on glass substrates with various MgO buffer layer thicknesses have been investigated. All the layers are deposited by plasma-assisted molecular beam epitaxy. Without the MgO buffer layer, surface cracks due to the difference in the thermal expansion coefficients between ZnO and the quartz substrate are easily observed. With the MgO buffer layer, the cracks drastically decrease. The surface morphology changes with different MgO buffer layer thicknesses due to the compressive-tensile stress balance. The ZnO films with a medium MgO buffer layer thickness show a dotlike surface. All samples except those with the dotlike surface exhibit c-axis oriented polycrystalline structures. The photoluminescence emission intensity is also improved by increasing the buffer layer thickness until the optimum MgO buffer layer thickness of approximately 150 nm is reached. Few cracks appear with the reduction of the photoluminescence (PL) intensity when the buffer layer thickness is more than the optimum value. All of the as-grown ZnO films without cracks exhibit n-type conductivity.

Improved conversion efficiency in dye-sensitized solar cells based on electrospun Al-doped ZnO nanofiber electrodes prepared by seed layer treatment

“…However, the asspun composite nanofibers can easily crack and peel away from the substrate after calcination due to the shrinking effect and poor adhesion, as previously reported for ZnO films [34]. To solve this problem, a seed layer (SD) can be introduced to improve the adhesion of the AZO nanofiber film to the FTO substrate.…”

Improvement of Flame-made ZnO Nanoparticulate Thick Film Morphology for Ethanol Sensing

“…The crack phenomenon can be described as follows. Firstly, the thermal expansion coefficients of the alumina substrate (∼ 7 × 10 -6 K -1 ) [ 80 ] and the ZnO (∼ 4.75 × 10 -6 K -1 ) [ 81 ] thick film were difference. Yamada et al [ 79 ] mentioned that the difference in the thermal expansion of the substrate and material film was one of the most important factors responsible for the cracking phenomena.…”

“…Yamada et al [ 79 ] mentioned that the difference in the thermal expansion of the substrate and material film was one of the most important factors responsible for the cracking phenomena. Also Deesirapipat et al [ 81 ] reported the thermal expansion coefficient mismatch between material and substrate indicating a differential expansion coefficient probably causing these cracks. Secondly, the ZnO thick films were annealed at different annealing temperatures using very fast heating rates and cooling rates to room temperature causing a tensile stress and probably of the crack formation.…”

Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

“…Moreover, several cracks can also be observed in the SEM of the AZO nanofiber films. During the calcination process, there is the difference in thermal expansion coefficients between ZnO film and the substrate, the tensile strain from the substrate affects the ZnO film and often results in the film cracking and peeling off [29]. Therefore, the strong stresses generated during the calcination process lead to the shrinkage of the AZO nanofiber, and thus cause the AZO nanofiber films to crack, as shown in Fig.…”