A method named synthesis, solute diffusion (SSD) has been developed for growing compound semiconductor crystals, GaP in particular, for light-emitting diode (LED) use. The grown crystal is cylindrically shaped and is composed of fairly large-size grains. Growth rate is limited by the diffusion process of phosphorus in the gallium melt. The diffusion coefficient was obtained from the growth rate and found to be 8×10 -5 cm 2 s -1 at 1100°C with an activation energy of 0.65 eV. Donor impurities, tellurium or sulfur, can be reproducibly incorporated from 3×10 17 to 4×10 18 cm -3 , with segregation coefficients at 1150°C, 0.038 and 1.0, respectively. The quality of the grown crystals was observed to be exceptionally good, and the saucer-type pits were hardly observable in the crystal on modified AB etching. Highly efficient red-light-emitting junctions were reproducibly grown by only one single-layer-single-liquid-epitaxy process, in which zinc was doped from the vapor phase. A double-layer-single-epitaxy process, which we call "liquid epitaxial grown-in junction" process, was also developed and it produced highly efficient green LED's. The LED's grown on the SSD wafers have efficiencies up to 7.4 percent for red and 0.15 percent for green.