Morphologies and plane indices of pyramid patterns on wet-etched patterned sapphire substrate

•This paper analyses the evolution of pyramids on the patterned sapphire substrate (PSS) during wet etching process.•The morphologies and indices of 18 pyramid facets were investigated.•When the SiO2 mask remained, pyramid covered with six facets.•When the SiO2 was etched away, three facets were exposed on the top of pyramid.•When etching increased, another six facets and three facets appeared.

A wet etching process was employed to investigate the evolution of pyramids on the patterned sapphire substrate (PSS). It has been found that the PSS comprised a hexagonal pyramid covered with six facets {34¯17} when disk-shaped SiO2 mask still remained. Three facets {11¯05} were exposed when mask was etched away. In this study, a continuous etching process was performed. It was found that another six facets {45¯130} and another three facets {11¯010} appeared on the bottom and the top of pyramid. Finally, when the etching time reached around 5 min, most of pyramids on the PSS disappeared.