Trap-mediated excitation of Er³⁺ photoluminescence in Er-implanted GaN

Site-selective photoluminescence (PL) spectra obtained at 6 K from the 1540 nm ⁴I_13/2→⁴I_15/2 emissions characteristic of four distinct Er³⁺ centers in Er-implanted films of GaN are compared with the Er³⁺ PL excited by 325 nm above-gap pump light. Two of the site-selective 1540 nm Er³⁺ PL spectra pumped by below-gap, trap-mediated excitation bands dominate the Er³⁺ PL spectrum excited by above-gap light. A third broad band-excited spectrum and a fourth spectrum pumped by direct Er³⁺ 4f-band absorption are apparently not strongly excited by above-gap light. These results indicate that trap-mediated excitation dominates above-gap pumping of Er³⁺ emission in GaN:Er, and suggest an explanation for the reduced thermal quenching of Er³⁺ emission in GaN.