Multicolor light-emitting diodes with double junction structure

A GaAs:Si-GaAsP heterostructure chip coated with NaYF4:Yb,Er phosphor has been fabricated to demonstrate multicolor operation. The one-chip light-emitting diodes (LED´s) with double junctions showed a centrosymmetrical distribution of green-and red-light intensities. An intermediate hue between green and red was achieved by adjusting the thickness of the phosphor. The luminance of each color was more than 100 fL at a current density of 30 A/cm²and the power efficiency was 2-3 × 10^-4for green. The luminance of the green light was less than 250 fL at 20 A/cm²for a single GaAs:Si LED because of the refraction of infrared light in the GaAsP layer.