The degree of incorporation of Pr, during liquid-phase epitaxy from a Ga-rich solution, was investigated by making low-temperature photoluminescence measurements. The photoluminescence spectra of undoped (background) epilayers exhibited 4 different peaks which were considered to be due to an intense transition between exciton and neutral donor, an intense transition between excitons and neutral acceptors, a transition in electron-acceptor recombination, and a weak transition which arose from donor-acceptor recombination. Variations in the above peaks, as a function of the degree of Pr doping, were studied in detail. In general, it was found that the photoluminescence spectra of low-Pr epilayers exhibited an obvious gettering effect upon the donor-related peaks. In the case of the spectra of high-Pr epilayers, a defect-related emission peak was produced. For the purposes of purification, a Pr doping of less than 0.05% was suggested. The electrical data also revealed that unwanted donor impurities were gettered by Pr ions during liquid phase epitaxial growth. On the other hand, Pr-related defects which formed in high-Pr melts could act as scattering centers and cause their mobilities to decrease.

G.C.Jiang, L.B.Chang, G.H.Chang, L.S.Lu: Journal of Crystal Growth, 1995, 152[3], 127-34