Quantum dots excited InGaN/GaN phosphor‐free white LEDs

Abstract

AbstractCommercial GaN based white LEDs have been fabricated using phosphor coating of blue LEDs. We report on the growth of InGaN/GaN based white LEDs using In‐rich InGaN quantum dots incorporated in the MQW layers. The photoluminescence spectrum of the MQWs shows a broad emission spectrum covering 400 to 700 nm. Cross‐section TEM shows the existence of pyramidal shaped quantum‐like structures with size of 1.5‐2.0 nm embedded in the InGaN well. To prevent the out‐diffusion of these InGaN quantum dots in the well layer during thermal activation of p‐GaN, a small amount of Indium was introduced into the p‐GaN and the temperature was kept below 800 °C for p‐InGaN epilayer growth. I‐V measurement of the white LEDs gives a forward voltage of 5.2 V for a current of IF ∼20mA. The chromaticity coordinate ranges from 0.28 < x,y < 0.34 with a colour temperature of ∼6000 K. The internal quantum efficiency was separately determined to be in excess of 50%. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)