Surface modification on wet-etched patterned sapphire substrates using plasma treatments for improved GaN crystal quality and LED performance

A surface-modified wet-etched pyramidal patterned sapphire substrate (PSS) was used to fabricate blue-light InGaN-based light-emitting diodes (LEDs). The pyramidal PSSs were modified using CF₄ plasma with different treatment times. It was found that the plasma treatment created a slightly roughened surface pattern, which not only suppressed lateral growth from the incline of the pattern, but also enhanced vertical growth from mesa and groove of the pattern. A clear reduction of GaN dislocation density in PSS LEDs was confirmed by electron microscopy, X-ray diffraction and etch-pit-density measurements. Additionally, the output power of plasma-treated PSS LEDs was 25 higher than that of untreated PSS LED for a 20 mA injection current. The enhanced output power was attributed to the reduction in dislocation density of the GaN film and the enhancement of light scattering by surface-modified PSSs.