Vapor Deposition of GaP for High-Efficiency Yellow Solid-State Lamps

Nitrogen-doped gallium phosphide has been epitaxially deposited on GaP substrates by chemical vapor deposition using phosphine, hydrogen chloride, and gallium as reactants. The morphology of the epitaxial layers and the electroluminescence of the Zn-diffused diodes were investigated as a function of substrate temperature, Ga source temperature, and reactant concentration. It was found that by decreasing the PH₃/GaCl ratio at which the material was grown, the electroluminescence of the diodes prepared from the material shifted to longer wavelengths as a result of increased nitrogen incorporation. Minority carrier lifetime for the n-type epitaxial material was measured by the diode reverse-recovery technique. For diffused diodes, the reciprocal of the minority carrier lifetime is directly proportional to the PH₃/GaCl ratio at which the material was prepared. Possible recombination centers consistent with lifetime-ambient composition behavior are the Si-0 complex or Ga vacancy complex. Quantum efficiencies for the encapsulated yellow light emitting diodes with a mesa structure were as high as 0.15% at 20 A/cm² and 0.24% under pulsed operation at 100 A/cm².