Observation of multiple Er³⁺ sites in Er-implanted GaN by site-selective photoluminescence excitation spectroscopy

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies have been carried out at 6 K on the 1540 nm ⁴I_13/2→⁴I_15/2 emission of Er³⁺ in Er-implanted films of GaN grown by metalorganic chemical vapor deposition. The PLE spectra exhibit several broad below-gap absorption bands, which excite three distinct site-selective Er³⁺ PL spectra. The excitation of two of the site-selective Er PL bands involves optical absorption by defects or background impurities, rather than direct intra-f shell absorption, with subsequent nonradiative transfer of the energy to nearby Er³⁺ luminescence centers. The characteristics of the PLE spectrum of the third site-selective PL band suggest that an exciton bound at an Er-related trap is involved in the excitation mechanism.