Control of the color contrast of a polychromatic light-emitting device with CdSe-ZnS nano-crystals on an InGaN-GaN quantum-well structure

Blue-red polychromatic light-emitting devices are fabricated by attaching red-emitting CdSe-ZnS nano-crystals on a blue-emitting InGaN-GaN multiple-quantum-well (MQW) structure. To improve the red/blue intensity contrast, holes of different diameters are fabricated for increasing the direct contact area between the MQW active regions and CdSe-ZnS nano-crystals. By comparing the devices of 10-, 50-, 60-, and 70-mum hole diameters, and a reference device of no hole, it is found that the hole diameter of 60 mum represents an optimized condition from the viewpoint of maintaining high quantum efficiency. However, the device of 10-mum holes has the highest red/blue intensity ratio, which corresponds to a 36% increase. This result is attributed to its largest side-wall area in the holes among various samples