Elucidation of the excitation mechanism of Tb ions doped in AlxGa1−xN grown by OMVPE toward a wavelength-stable green emitter.

The trivalent terbium ion (Tb³⁺) emits ultra-stable visible light consisting of blue, green, yellow, and red. Tb-doped semiconductors are candidates for novel full-color light sources in next-generation displays. Particularly, Tb-doped Al_xGa_1−xN (Al_xGa_1−xN:Tb) has attracted much attention for device applications. We present the luminescence properties of Al_xGa_1−xN:Tb grown by the organometallic vapor phase epitaxy. At 15 K, emission related to the ⁵D₄–⁷F_J (J = 3, 4, 5, 6) transitions is observed for Al_xGa_1−xN:Tb with x ≥ 0.03. Thermal quenching of emission originating from the ⁵D₄–⁷F_J transition is suppressed for higher Al compositions, and the luminescence is clearly observed at room temperature for Al_xGa_1−xN:Tb with x ≥ 0.06. The small thermal quenching is attributed to the enhanced excitation to the ⁵D₄ level of Tb³⁺ ions via the 4f–5d transition and not due to the suppression of energy back-transfer paths in excited Tb³⁺ ions. Although additional emission originating from the ⁵D₃–⁷F_J transitions is observed at 15 K for Al_xGa_1−xN:Tb with x ≥ 0.15, it is not observed at room temperature because the excitation to the ⁵D₃ level via the 4f–5d transition is less efficient at high temperature. For Al_0.15Ga_0.85N:Tb, monochromatic green light is demonstrated using a SiO₂/ZrO₂ distributed Bragg reflector. [ABSTRACT FROM AUTHOR]