We report on the study of impact excitation of Er ions in GaAs. The me
talorganic chemical vapor deposition grown, p+-n structured electrolum
inescence (EL) devices were fabricated by growing, at different temper
atures, GaAs:Er layers on top of the n+ GaAs substrates. P+ layers of
GaAs were made by Zn diffusion from the top surfaces. When we forward
biased these diodes, the EL spectra were similar to the respective pho
toluminescence (PL) spectra of each sample. The spectra of the samples
differed for the various growth temperatures. However, when we revers
e biased these diodes, the EL spectra are the same for all samples but
different from the PL spectra. These results indicate that the Er cen
ter(s) excited by direct impact is different from the Er center(s) exc
ited through electron-hold recombination and the subsequent energy tra
nsfer.