This study investigated the influence of high-quality AlN templates on the internal quantum efficiency (IQE) of AlGaN-based multiple quantum wells (MQWs) using photoluminescence spectroscopy. An extremely high IQE of 90% at room temperature was obtained from MQWs on face-to-face annealed sputter-deposited AlN/sapphire templates. The dependence of efficiency curves on temperature indicated that nonradiative recombination centers were almost fully saturated under higher excitation power densities even at 400 K. Moreover, analysis of the efficiency curves using a rate equation model based on exciton recombination processes suggested that radiative recombination was the dominant recombination process even at 400 K.

The correlation between the internal quantum efficiency (IQE) and the effective diffusion length estimated by the cathodoluminescence intensity line profile near the dark spots, including the effect of non-radiative recombination due to point defects, was experimentally clarified for AlGaN multiple quantum wells (MQWs) on face-to-face annealed (FFA) sputter-deposited AlN templates with different IQEs and similar dislocation densities. The IQEs, which were determined by temperature- and excitation-power-dependent photoluminescence measurements, were independent of the dark spot densities and increased with increasing effective diffusion length (Leff) estimated from the cathodoluminescence line profile analysis. These results suggested that the IQEs of the MQW/FFA samples were governed by the point defect density. The fitting results for the relationship between IQE and Leff and for that between IQE and Cmax explained the experimental results qualitatively.