Traditional approaches include colour down-conversions, combining high energy LEDs emitting in the blue or near ultra-violet band with a mix of phosphors that re-emit at different wavelengths. Generally, this approach emulates an incomplete white light spectrum at a lesser quantum efficiency than the original emitter (the LED covered in phosphor). The phosphors' limited lifetime compared to that of the actual LED illuminating them can also negatively impact the overall longevity of the white light.
Other solutions combine multiple LED dies emitting at different peak wavelengths, but here again, white is a short-lived illusion, missing out on the natural continuum of true white light.
A team of researchers from the University of Hong Kong is confident broadband white light could be obtained from monolithic LED dies. In their recently published ACS Photonics paper "Monolithic Broadband InGaN Light-Emitting Diode", the researchers disclose promising results using high indium content InGaN-GaN quantum well structures grown on a sapphire substrate.
The whole stack is then etched-through using a mix of silica nano-particles as a mask layer, leaving a mix of nano-pillar patterns throughout the LED die, ranging from nanotips about 150nm in diameter to microdisks about 7μm in diameter.