Light extraction study on thin-film GaN light-emitting diodes with electrodes covering by wafer bonding and textured surfaces

Textured n-side-up GaN LEDs with interdigitated imbedded electrodes (IIEs), high-reflection mirror, and double-side roughening on both p-GaN and undoped-GaN layers are investigated. The IIE structure can eliminate electrode shading. The epitaxial layers of the devices are grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The devices are subsequently fabricated with wafer bonding, laser lift off, and chemical dry/wet etching techniques. The n-side-up structure is useful for enhancing light extraction and increasing light output power. Luminance intensity performance (at 350-mA injection current) is 160% and 20% higher than those of the conventional structure and the p-side-up structure with high-reflection mirror on silicon substrate and with electrode shading, respectively. The performance of p-side-up glue bonding LED (at 350-mA injection current) is only 120% higher than the conventional structure. The light extraction efficiency of n-side-up thin-film LEDs is better than that of p-side-up thin-film LEDs.