Conventional white LEDs use yellow phosphors.
High unit cost due to combination of multi-colored LED chips

A research team at KAIST has developed a white LED manufacturing technology. This technology, which does not use phosphors, is expected to contribute to the advancement of next-generation lighting and display technologies.

Currently, most white LEDs utilize a blue LED with a yellow phosphor, or combine multiple colored LED chips. However, this method of combining multiple colored LED chips in parallel has the disadvantage of higher unit costs. Furthermore, the yellow phosphor is a rare earth element, leading to a high dependence on imports and limitations such as low color rendering and discoloration.

Accordingly, a research team led by Professor Cho Yong-hoon of the Department of Physics at KAIST has devised a method for producing a white LED using a single semiconductor chip, without the use of phosphors. They designed a microcomposite structure that resembles a pyramid with a concentrically cut-off top.


Schematic diagram of a micro-sized truncated pyramid-shaped composite structure that emits white light by current injection without using a phosphor.
(Image: Provided by KAIST)

Through the change of three-dimensional structure area control
White LED demonstration with a single chip

This microscopic three-dimensional structure forms quantum wells with different conditions on each face, allowing each face to emit light of a different color. Ultimately, this allows for the mixing of various colors within a single structure, eliminating the need to combine multiple LED colors. By controlling the time and conditions for creating a three-dimensional structure and changing the area of each crystal plane, LEDs with various mixed colors can be produced.

The research team demonstrated a phosphor-free white LED using a single LED chip by adjusting the area of each crystal plane. Furthermore, the color remained virtually unchanged even when the current applied to the LED was varied. This represents an early stage of phosphor-free white LEDs and is significant in that it suggests a direction for future phosphor-free white light sources.

Professor Cho said, "If efficiency is improved through future 3D semiconductor process development, it could be used as a single-chip white light source that is inexpensive and offers excellent color reproducibility without the need for phosphors." Meanwhile, this research was published online on the 12th in the journal "Light: Science & Applications," published by Nature, and its importance was recognized, leading to its selection as the cover paper for the print edition.