Temperature-independent optical transition with sub-nanometer linewidth in thermally diffused Gadolinium in GaN.

We have demonstrated temperature-independent optical transitions from thermally diffused Gd in GaN. The emission wavelength is sub-bandgap with respect to GaN. The origin of photon generation is identified as atomic transitions in Gd hosted in the weak interaction field of GaN. The emission linewidth remains sub-nanometer (0.1-0.6 nm) from 19 to 300 K for all the optical pumping intensities. The shift in wavelength with temperature and optical pumping is negligible (∼0.8  nm) for the entire temperature window. The output intensity is found to scale linearly with the pumping power. The magnetic, electrical, and physical characterizations indicate that Gd acts as an electron trap in GaN. Transient absorption spectroscopy discovers a major nonradiative parallel path for carrier leaking. The observed characteristics may find potential applications in narrow linewidth optical sources.