Progress in Preparation of Patterned Sapphire Substrate for GaN-based Light Emitting Diodes

GaN-based light emitting diodes are extensively used for light emitting diodes in the green to ultraviolet (UV) wavelength region and have already been widely used in traffic signals, outdoor displays, full-color displays and back lighting in liquid-crystal displays. Although GaN-based light emitting diodes are commercially available, it is still difficult to manufacture highly efficient GaN-based light emitting diodes due to the high dislocation density and the low light extraction efficiency. Patterned sapphire substrates for GaN-based light-emitting diodes have attracted much interest in recent years because it can not only reduce the threading dislocation density of epitaxial GaN films, but also improve the light extraction efficiency of GaN-based light-emitting diodes. A comprehensive review is presented on the mechanisms responding for performance enhancement of GaN-based light emitting diodes on patterned sapphire substrates, methods of preparing patterned sapphire substrates and pattern-size of patterned sapphire substrates. What is more, improved performance of GaN-based light-emitting diodes on patterned sapphire substrates prepared by different methods and pattern-size are further discussed in detail. In view of the existing problems, the prospects for future development of patterned sapphire substrates are also proposed.