Abstract
Effect of holding time after covering the substrate with epitaxy solution in n-on-p liquid-phase epitaxy of GaP red-emitting diodes is investigated. Emission efficiency increases sharply with increasing the holding time, reaches a maximum at 15–25 min. and then decreases. From measurements of the diodes photocurrent, this variation is shown to be due to the variation of Zn-O luminescent center concentration in the light-emitting region, and is explained by two competing processes. At a short holding time, the etching rate of the substrate surface in slightly unsaturated epitaxy solution is faster than the out-diffusion rate of zinc from the substrate surface. The surface layer deteriorated by preheating is then removed faster than it extends inward, and hence zinc and Zn-O pair concentrations in the active region increase with holding time. At a long holding time, the etching rate becomes slower than the diffusion rate, and zinc and Zn-O pair concentrations decrease.