Tilted Quantum Wells Produce Rainbow of Colors

Anne L. Fischer

In pursuit of nitride-based white LEDs, scientists at Kyoto University and at Nichia Corp.’s Nitride Semiconductor Research Laboratory in Tokushima, both in Japan, have achieved a rainbow of colors from InGaN/GaN quantum wells tilted 56° with respect to the surface of the sapphire substrate on which they are grown.

The researchers use microstructured GaN epilayers as templates for device fabrication. The indium composition in the tilted slope gradually changes, redshifting the emission across the structure and producing the continuous spectrum across the visible range. The spectral distribution can be changed by altering the degree of the gradient, which is determined by the growth conditions.

The work may find application in the development of white LEDs. Yoichi Kawakami, an associate professor at the university, said that white LEDs based on the tilted quantum wells would be expected to offer higher luminous efficacies than those that rely on stimulated phosphors, which are limited by Stokes loss.

The scientists will continue the research by sandwiching the rainbow-emitting active layers between P- and N-type cladding layers, and then will assess the performance of the LEDs.

Applied Physics Letters, Dec. 5, 2005, 231901.