Fabrication of deep UV LEDs with a high-quality AlGaN on face-to-face annealed sputter-deposited AlN template

To fabricate deep-ultraviolet(DUV)-LEDs with high efficiency, the crystallinity of AlGaN must be improved, and is significantly influenced by that of the underlying AlN template. The face-to-face annealed sputter-deposited AlN templates (FFA Sp-AlN) on sapphire have achieved screw- and edge-dislocation densities (TDDs) of 10^4 cm^-2 and 10^7cm^-2. Reduction of TDDs in FFA Sp-AlN and surface flattening of AlxGa1−xN grown on the FFA Sp-AlN play important roles to achieve a high external quantum efficiency (EQE). After the MOVPE homoepitaxial growth of AlN, the FFA Sp-AlN exhibits ideally smooth surface morphology. The EQE of the UV-C LED fabricated on FFA Sp-AlN increased with the TDD reduction of the FFA Sp-AlN. Maximum EQE of 8.0% and output power of 6.6 mW at a 20-mA input were achieved with the peak emission wavelength of 263 nm. We also fabricated 230 nm and 236 nm LEDs on the FFA Sp-AlN templates.