Development of c-plane thin-film flip-chip LEDs fabricated by photoelectrochemical (PEC) liftoff

We report a novel thin-film flip-chip (TF-FC) c-plane GaN LED design grown on bulk GaN. By way of a photoelectrochemical (PEC) undercut etch, LEDs are transferred from a bulk GaN substrate to a sapphire submount. As a first demonstration, the resulting LEDs have threshold voltages below 3V and a peak external quantum efficiency (EQE) of 8.4% at a wavelength of 471 nm. These results are of LEDs without any growth and light extraction optimizations. Based on ray tracing modeling, light extraction of these LEDs is 25.1%. By roughening the N-face and incorporating a reflective silver mirror, the light extraction will improve to 75.5% based on modeling results. This threefold increase is expected to be reflected in an improvement in the EQE as well.