The luminescence of p-type GaP(Zn,O), a semiconducting material for light emitting diodes, is controlled by the transitions of the excited free electrons and by those of the electrons bound to the luminescent nearest-neighbor (ZncaOp) complexes. The results of the determination of the internal quantum efficiency (~l) on a large number of samples, prepared by solution growth and by liquid phase epitaxy and covering a zinc concentration range of 1027-5 9 10 is cm -~, lead to the conclusion that an Auger effect acting on the bound electrons is the dominant cause of the reduction of the internal efficiency of the samples with a free hole concentration (p) above 4 9 1017 cm -~, where also the trapping by "killers" becomes negligible. The Auger constant was derived, being ~3 9 10 -11 cm 3 sec -1. Below this concentration the thermalization of the electrons bound to the complexes is the more important effect enhancing the otherwise relatively small action of the killers. The best value for ~ is ~40% at p ~5 9 1017 cm-~. Decay time (~) measurements, using pulsed and sine-wave modulated excitation, provide insight in the effect of screening by free holes on the radiative and Auger transitions by using in the interpretation of the data the quantity (m/T) which is proportional to the effective radiative recombination rate (including the effect of screening mentioned). Both radiative and Auger transition probabilities are reduced by a common screening factor as low as 0.2. Electron diffusion length measurements on the epitaxial samples show a strong decrease of the minority carrier lifetime with increasing zinc concentration which is ascribed mainly to the trapping by the (ZnO) complexes whose concentration increases with the zinc dolce. This study also provides information on the oxygen incorporation during the crystal growth. This incorporation probably takes place at thermal equilibrium between the oxygen source and the solid GaP.[O] increases with [Zn] reaching ~10 is cm -3 at [Zn] ~ 5. 10 is cm-~.Semiconductor diodes that emit visible light are of increasing importance for certain applications, i.e., for indication and for display of symbols. The luminescence efficiency of such diodes is generally much below 100%. Various causes exist for this circumstance part of which are peculiar to the semiconductor material used and to the devices made from them. These causes are still a matter oi conjecture. In this respect the subject of this paper, p-type gallium phosphide doped with zinc and oxygen, is no exception. Partly these causes arise from the properties of the light emitting layer, i.e., p-type GaP(Zn, O). Another cause, generally of minor importance for this type of material, is the limited efficiency of injection of electrons into this layer.A study of dopant-dependent recombination in ptype GaP(Zn, O) is useful to elucidate the relevant properties of this layer with respect to both bulk efficiency and injection efficiency.With regard to the bulk efficiency results have been published by Dishman, DiDomenico, and Carus...