The red electroluminescence in gallium phosphide at the maximum quantum efficiency is a constant, independent of injection efficiency, for a series of liquid-phase epitaxially grown diodes which have common Zn- and O-doped p-type substrates and variable Te-doped n-type layers. This behavior and the subsequent decrease in quantum efficiency with increasing diode current are both explained in terms of the saturation of Zn-O complexes by captured electrons in the p region.