Study on the morphology and shape control of volcano-shaped patterned sapphire substrates fabricated by imprinting and wet etching

A volcano-shaped patterned sapphire substrate (VPSS) was fabricated by imprinting lithography and wet etching to enhance the light output of LED devices. A hexagonally arranged pattern with different crystal orientations was imprinted onto the sapphire substrate. As the etching time increased, the pattern with a crater in its center was changed from truncated triangular pyramids to truncated hexagonal pyramids with symmetrical sidewall facets. Small craters surrounded by three {1 (1) over bar 08} facets appeared with 3-fold or 6-fold symmetry at the boundaries with neighboring pyramids. The mechanism of sapphire wet etching for VPSS synthesis was correlated to thermodynamics limits and the SiO2 mask pattern. The as-fabricated VPSS with slant angles of 34.3 degrees and 69.9 degrees was considered to enhance the internal quantum efficiency (IQE) and light extraction efficiency (LEE) of GaN-based LEDs.