Annealing studies of photoluminescence spectra from multiple Er³⁺ centers in Er-implanted GaN

A study of selectively excited photoluminescence (PL) at approximately 6 K in Er-implanted GaN as a function of annealing temperature (400-1000 °C) has detected nine different Er³⁺ centers with distinct approximately 1540 nm ⁴I_13/2→⁴I_15/2 Er³⁺ PL spectra and different activation temperatures. However, most of the optically active implanted Er atoms are incorporated at annealing temperatures as low as 400 °C on a single type of center for which PL can only be excited efficiently by direct intra-4f shell absorption and is not strongly pumped by either above-gap or broad-band below-gap absorption. This strongly suggests that this high-concentration Er³⁺ center is an isolated, isoelectronic center consistent with Er³⁺ substituted on a Ga site. In contrast, a very small fraction of the Er atoms that form a variety of Er-defect/impurity complexes dominate the Er³⁺ emission spectra excited by above-gap and broad-band below-gap absorption because of their larger cross sections for both carrier capture and optical absorption.