Electrically driven, phosphor-free, white light-emitting diodes using gallium nitride-based double concentric truncated pyramid structures

White light-emitting diodes (LEDs) are becoming an alternative general light source, with huge energy savings compared to conventional lighting. However, white LEDs using phosphor(s) suffer from unavoidable Stokes energy converting losses, higher manufacturing cost, and reduced thermal stability. Here, we demonstrate electrically driven, phosphor-free, white LEDs based on three-dimensional gallium nitride structures with double concentric truncated hexagonal pyramids. The electroluminescence spectra are stable with varying current. The origin of the emission wavelength is studied by cathodoluminescence and high-angle annular dark field scanning transmission electron microscopy experiments. Spatial variation of the carrier injection efficiency is also investigated by a comparative analysis between spatially resolved photoluminescence and electroluminescence. Phosphor-free white light-emitting diodes (LEDs) are realized that are based on gallium nitride (GaN) structures and exhibit stable color emission. White LEDs are fast replacing conventional lighting due to the very significant energy savings they offer, but phosphor-based white LEDs suffer from inherent conversion losses, high manufacturing cost, and poor thermal stability. Now, Yong-Hoon Cho and co-workers at Korea Advanced Institute of Science and Technology (KAIST) in South Korea have demonstrated electrically driven phosphor-free white LEDs with stable color emission. The LEDs contain gallium nitride structures with double concentric truncated hexagonal pyramids grown by metal-organic vapor-phase epitaxy. Each facet of a pyramid emits a different wavelength. The LEDs were found to consistently emit white light with relatively stable CIE color coordinates when the injection current was varied.