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 metal-organic 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.