Effects of material growth technique and Mg doping on Er³⁺ photoluminescence in Er-implanted GaN

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies have been carried out at 6 K on the ∼1540 nm ⁴I_13/2-⁴I_15/2 emissions of Er³⁺ in Er-implanted and annealed GaN. These studies revealed the existence of multiple Er³⁺ centers and associated PL spectra in Er-implanted GaN films grown by metalorganic chemical vapor deposition, hydride vapor phase epitaxy, and molecular beam epitaxy. The results demonstrate that the multiple Er³⁺PL centers and below-gap defect-related absorption bands by which they are selectively excited are universal features of Er-implanted GaN grown by different techniques. It is suggested that implantation-induced defects common to all the GaN samples are responsible for the Er site distortions that give rise to the distinctive, selectively excited Er³⁺PL spectra. The investigations of selectively excited Er³⁺PL and PLE spectra have also been extended to Er-implanted samples of Mg-doped GaN grown by various techniques. In each of these samples, the so-called violet-pumped Er³⁺PL band and its associated broad violet PLE band are significantly enhanced relative to the PL and PLE of the other selectively excited Er³⁺PL centers. More importantly, the violet-pumped Er³⁺PL spectrum dominates the above-gap excited Er³⁺PL spectrum of Er-implanted Mg-doped GaN, whereas it was unobservable under above-gap excitation in Er-implanted undoped GaN. These results confirm the hypothesis that appropriate codopants can increase the efficiency of trap-mediated above-gap excitation of Er³⁺ emission in Er-implanted GaN.