Enhanced light output power of green LEDs employing AlGaN interlayer in InGaN/GaN MQW structure on sapphire (0001) substrate



In order to enhance light output power of green light-emitting diodes (LEDs) on a sapphire (0001) substrate, we employ 1.5 nm-thick AlGaN interlayer between an InGaN well layer and an upper GaN barrier layer. AlGaN interlayer controls asymmetric band profile due to piezoelectric field, and thus it controls the quantum-confined Stark effect. Although both photoluminescence intensity and electroluminescence intensity of a conventional MQW decreases drastically as the emission wavelength becomes longer, the intensity drop at spectral range of 530–580 nm is suppressed by utilizing an AlGaN interlayer. The maximum light output power of 12 mW at 532 nm and external quantum efficiency of 25.4% have been achieved for the LED employing Al0.30Ga0.70N interlayer at a driving current of 20 mA. This result indicates that the band-engineering approach is effective for an IQE enhancement at pure green or longer wavelength, even if a polar (0001) face is utilized.