Enhanced extraction and efficiency of blue light-emitting diodes prepared using two-step-etched patterned sapphire substrates

Using a hot acid wet etching method, we have fabricated two types of patterned sapphire substrates: A pyramidal patterned sapphire substrate (PPSS) and a flat-top patterned sapphire substrate (FTPSS). After placing these samples into an atmospheric pressure metallorganic chemical vapor deposition system, we deposited standard InGaN light-emitting diode (LED) structures onto their surfaces. The crystal quality of these two surfaces was enhanced, as evidenced using X-ray diffraction (the full width at half-maximum decreased from 406.8 arcsec for the conventional sapphire to 356.4 and 349.2 arcsec for the PPSS and FTPSS samples, respectively). The output power of InGaN-based blue LEDs incorporating the PPSS and FTPSS improved to 17.9 and 18.7%, respectively, at 20 mA.