Cascade single-chip phosphor-free white light-emitting diodes

In order to resolve the problems existing in the conventional phosphor-converted light-emitting-diodes (LEDs) and red-green-blue LEDs, the cascade single-chip phosphor-free white LED was proposed with GaAs∕GaN heterojunction direct wafer bonding. Corresponding to the color-matching calculation, the white LED demonstrated the CIE chromaticity coordinates of about (0.3, 0.3) at 20mA, which was very close to the ideal white light position (1∕3, 1∕3) on the chromaticity diagram. The fabrication and the electrical and optical performances of such white LEDs were described.