LAUSR

The light to be trapped inside light-emitting diodes (LEDs) greatly affects the luminous efficiency and device lifetime. Abrupt difference in refractive index between the sapphire substrate and GaN-based LEDs causes the light trapping by total internal reflection, however, its optical loss has been received for granted. In this study, we demonstrated the nanoporous GaN can be used as a refractive-index-matching layer to enhance the light transmittance at the sapphire-GaN interface in InGaN/GaN flip-chip light-emitting diodes (FCLEDs). The porosity and the refractive index of the nanoporous GaN layer were controlled by electrochemical etching of n-type GaN layer. The optical output power of FCLEDs with the nanoporous GaN layer grown on flat and patterned sapphire substrates was increased by 355% and 65% at an injection current of 20 mA, respectively, compared with that of an FCLED without the nanoporous GaN layer. The remarkable enhancement of optical output was mostly attributed to the nanoporous GaN layer which drastically increases the light extraction efficiency by decreasing the reflection of light at the sapphire-GaN interface.