Maskless roughening of sapphire substrates for enhanced light extraction of nitride based blue LEDs

A simple wet etching method based on the use of hot sulphuric (H2SO4) acid for roughening of the backside of the sapphire substrates for creating light scattering objects without any lithography processes is described. Scanning electron microscope images show that this method offers a possibility to tailor the size of the scattering objects by varying the treatment time. A metal organic vapor phase epitaxy (MOVPE) grown light emitting diode (LED) structure having a roughened sapphire backside exhibits a 20–25% increase of the electroluminescence output power compared to a reference sample on the standard c-plane sapphire at the operating wavelength of 460 nm.