Green and yellow emitting devices in vapor-grown gallium phosphide

Green and yellow emitting diodes can be made in nitrogen-doped gallium phosphide by a simple vapor-growth and diffusion process. The color is controlled by the nitrogen concentration, and bright yellow emission is made possible at room temperatures by the high nitrogen concentrations attainable in the vapor-growth process. As there are no problems of mismatch and strain in the homoepitaxial growth process, epitaxial layers can be thin and diffusion is straightforward. Typical yellow encapsulated diode efficiencies are around 0.05 percent, best results being 0.1 percent. The transparency of the substrate to the yellow emission allows diodes to be inverted, the improved heat sinking of the devices then permitting high current densities and very high brightnesses. Both green and yellow monolithic array structures can be made by localized diffusion techniques. Optical crosstalk is appreciable in the yellow emitting arrays and appropriate designs are required to improve contrast. Device life is evidently long at current densities in the range 1-100 A/cm 2 , and no catastrophic degradation is seen even at current densities in excess of 10 3 A/cm 2 .