Effective Color Conversion of GaN-Based LEDs via Coated Phosphor Layers

Gallium nitride (GaN)-based light-emitting diodes (LEDs) equipped with distributed Bragg reflectors (DBR) and covered with either red or green phosphor layers are fabricated to form quasi-monochromatic red or green light sources. Titanium oxide and silicon oxide layers are alternately deposited to form the DBR with high reflectivity of 94.6% at 450 nm on the top of the GaN LEDs. The upward propagating blue light is reflected back by the DBR to excite the red or green phosphor layer at the bottom of GaN LEDs, producing additional fluorescence. However, there is still some blue light emitted out from the DBR and the side wall of the LEDs. Therefore, to obtain more intensive and pure monochromatic red or green light, another red (or green) phosphor thin layer is coated on the DBR. Thus, fabricated LEDs with phosphor layers on both the top and bottom surface show satisfactory monochromaticity and conversion efficiency.