Formation of randomly dispersed pores in Ga-doped ZnO between Al2O3 and glass via promoted atomic diffusion: Experimental and computational study

• Porous Ga-doped ZnO layers are fabricated via Kirkendall effect-based diffusion.
• The pores are formed not only near the interface but also in the internal layers.
• The features of the nanopores in the layers depend on Ga doping concentration.
• Grain boundary promotes the atomic diffusivity and acts as the seeds of the pores.
• Ga doping induces the mechanical stresses and affects the growth rate of pores.

Kirkendall diffusion, an unbalanced interdiffusion process through an interface of two materials, has attracted attention for decades as one of the promising techniques to fabricate nanoporous materials. In particular, a lot of efforts have been focused on the study of Kirkendall diffusion occurred in ZnO-based material couples due to the unique optoelectronic properties of ZnO. In this study, we fabricate nanoporous planar multilayered structures composed of Al2O3/Ga-doped ZnO (GZO)/Glass with different Ga concentrations by utilizing Kirkendall effect-induced diffusion. It is demonstrated that Ga-doping leads to the formation of internal (not interfacial) voids in the GZO layers, and the features of formed voids clearly depend on the Ga concentration. Through atomistic computational analyses, we elucidate that grain boundaries (GBs) whose density increases as the Ga doping concentration increases promote the local atomic diffusivity, and consequently act as the initiators of voids formed in the GZO layers. In addition, the doped Ga atoms and GBs induce a compressive stress within the GZO layers, which suppresses the growth rate of each individual void. Fundamental understandings of atomic diffusion mechanism demonstrated in this study may provide a simple approach to fabricate nanoporous materials with controlled porosity by modulating the Ga doping concentration.

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