  We report the quantum efficiency of photoluminescence processes of Er optical
centers as well as the thermal quenching mechanism in GaN epilayers prepared by
metal-organic chemical vapor deposition. High resolution infrared spectroscopy
and temperature dependence measurements of photoluminescence intensity from Er
ions in GaN under resonant excitation excitations were performed. Data provide
a picture of the thermal quenching processes and activation energy levels. By
comparing the photoluminescence from Er ions in the epilayer with a reference
sample of Er-doped SiO2, we find that the fraction of Er ions that emits photon
at 1.54 micron upon a resonant optical excitation is approximately 68%. This
result presents a significant step in the realization of GaN:Er epilayers as an
optical gain medium at 1.54 micron.
