We report on the optical properties of the InGaN-based red LED grown on a c-plane sapphire substrate. Blue emission due to phase separation was successfully reduced in the red LED with an active layer consisting of 4-period InGaN multiple quantum wells embedding an AlGaN interlayer with the Al content of 90% on each quantum well. The light output power and external quantum efficiency at a dc current of 20 mA were 1.1 mW and 2.9% with the wavelength of 629 nm, respectively. This is the first demonstration of a nitride-based red LED with the light output power exceeding 1 mW at 20 mA.

High-efficiency InGaN light-emitting diodes (LEDs) in the “green gap” range were fabricated on c-face sapphire (0001) substrates. Optical properties were enhanced by band engineering of active layers and optimization of growth conditions. Output power and external quantum efficiency of 11.0 mW and 24.7% for a 559 nm green-yellow LED and 4.7 mW and 13.3% for a 576 nm yellow LED with the injection current of 20 mA were achieved, respectively.

We developed a green-emitting phosphor Sr 3 Si 13 Al 3 O 2 N 21 :Eu 2þ that is highly luminescent under excitation by blue light. It shows a highly efficient green luminescence whose external quantum efficiency reaches 67% for 460 nm excitation, and has small thermal quenching. Using this phosphor, we obtained white light-emitting diodes (LEDs) whose luminous efficacy and color rendering index R a at 5330 K are 62 lm/W and 87, respectively. These features show that this green-emitting phosphor has high potential for application to white LEDs.

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 Al 0.30 Ga 0.70 N 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.

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the <11*BAR*2*BAR*0> direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical calculation. A single peak emisson, at a wavelength of 417.5 nm, with a full width at half-maximum of 0.15 nm, was obtained. The threshold current density of the laser was 50 kA/cm2 and a voltage for the threshold current was 20 V.