Effect of the Donor Concentration on the Green Electroluminescence from Gallium Phosphide Diodes

Abstract

The optical properties of gallium phosphide green electroluminescent diodes formed by the in-diffusion of zinc or beryllium into sulfur-doped vapor-phase epitaxial gallium phosphide have been studied as a function of donor concentration at temperatures between 77° to 350°K. At 77°K shallow-donor-shallow-acceptor pair emission dominated for all diodes at high currents. At room temperature, bound exciton emission involving residual nitrogen impurities was dominant for lightly doped samples, while shallow-donor-valence-band emission was dominant for samples with a donor concentration greater than 8×1017 cm−3. For both types of emission, the intensity at 300°K varied as exp (qV/kT). Relatively low efficiencies appeared to be a result of short nonradiative lifetimes in the vapor-grown GaP. Electron microprobe measurements verified that variations in the positions of the emission lines from crystal to crystal were due to As contamination. An acceptor ionization energy of 56 meV was deduced for beryllium from a study of the low-temperature emission spectra.