Analysis of Wet-Etched Structures on R-Plane Substrates of Sapphire in the Etchant of Sulfuric Acid and Phosphoric Acid

The occurrence and variation of wet-etched structures on R-plane substrates of sapphire were analyzed according to the distribution of drilling rates of typical crystal planes. First, the experiment for etching the sapphire hemisphere was conducted to obtain the distribution of etching rates with C-plane as the rotation center in the experimental etchant (236 °C, three parts H₂SO₄ and one part H₃PO₄ in terms of volume). Then, the transfer matrix was applied to transform the distribution of etching rates with C-plane as the rotation center in the experimental etchant (236 °C, three parts H₂SO₄ and one part H₃PO₄ in terms of volume) into the distribution of etching rates with R-plane as the rotation center. The positive curvature maximum identification method was then applied to obtain the distribution of drilling rates of typical crystal planes on R-plane substrates. Finally, the occurrence and variation of polygonal grooves with different mask configurations on R-plane substrates in the experimental etchant (236 °C, three parts H₂SO₄ and one part H₃PO₄ in terms of volume) were analyzed based on the distribution of drilling rates of typical crystal planes. This provides a basis for the application and development of GaN-based light-emitting diode devices.