Site-selective photoluminescence excitation and photoluminescence spectroscopy of Er-implanted wurtzite GaN

Site-selective photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been carried out at 6K on the ≈1540 nm ⁴I_13/2 → ⁴I_15/2 emissions of Er³⁺ in Er-implanted GaN. The PLE spectra exhibit several broad, below-gap, defect- or impurity-related absorption bands which excite three distinct site-selective Er³⁺ PL spectra. The near-band edge spectral position and lineshape of the PLE spectrum of one of the site-selective PL bands suggest that this Er site forms a trap level within the band gap and an exciton bound at this trap is involved in the excitation mechanism. In addition, high resolution PLE spectra obtained whh a tunable laser in the 810 nm spectral range reveal a set of sharp PLE peaks due to the ⁴I_15/2 → ⁴I_9/2 internal Er³⁺ f-band absorption superimposed on the broad defect PLE band. The site-selective PL spectrum exceed by the sharp line ≈810 nm Er³⁺ intra-f shell PLE bands is characteristic of a fourth distinct Er³⁺ site. The simple structure of the site-selective PL and PLE spectra associated with direct intra-fshell absorption suggests that the optically active Er site responsible for these spectra is of high symmetry in wurtzite GaN and that it could be attributed to a single Er atom on a Ga site.