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Regarding deep-ultraviolet optical device applications, face-to-face annealed sputter-deposited AlN (FFA Sp-AlN) is a promising alternative to the conventional metalorganic vapor phase epitaxy (MOVPE)-prepared AlN templates on sapphire substrates. However, FFA Sp-AlN tends to exhibit AlGaN growth-related hillock generation and surface morphology deterioration. In this study, we optimized the sputter-deposition conditions for AlN and MOVPE growth conditions for AlGaN to respectively reduce hillock density and size. After confirming AlGaN surface-flattening, we fabricated 263 nm wavelength UV-C LEDs on the FFA Sp-AlN and achieved maximum external quantum efficiencies of approximately 4.9% and 8.0% without and with silicone encapsulation, respectively.

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.

Thermal cycle annealing (TCA) is introduced to accelerate the dislocation annihilation in sputter-deposited AlN films on sapphire. Compared with constant temperature annealing, AlN films processed by TCA showed lower dislocation densities, smoother surface morphology, and fewer defects generated from the AlN/sapphire interface. After optimizing the film thickness, AlN films with a thickness of 800 nm, and X-ray rocking curve full widths at half maximum of 10–20 arcsec (0002) and 80–90 arcsec (10-12) were demonstrated, providing a simple and low-cost way to prepare high-quality AlN/sapphire templates for high-performance ultraviolet light-emitting diodes.

Combination of sputter deposition and high-temperature annealing is a promising technique for preparing AlN templates with a low threading dislocation density (TDD) at a lower film thickness compared to those prepared by the conventional metalorganic vapor phase epitaxy. However, cracking of AlN films during annealing is a critical issue. In this study, we controlled the residual stress of the sputter-deposited AlN films by modifying the sputtering conditions. Consequently, the occurrence of cracking was effectively suppressed. By optimizing the fabricating conditions, a TDD of 2.07 × 108 cm−2 was achieved for the AlN template with a thickness of 480 nm.