We increased the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) by introducing a highly reflective photonic crystal (HR-PhC) into the surface of the p-AlGaN contact layer, thereby achieving a high external quantum efficiency (EQE). A low-damage HR-PhC with a lattice period of approximately 250 nm was fabricated using nanoimprinting and dry etching. A reflective Ni/Mg p-type electrode was deposited on the HR-PhC layer using a tilted-evaporation method. The EQE of a conventional DUV LED with emission around 283 nm was increased from 4.8 to 10% by introducing the HR-PhC and the reflective Ni/Mg electrode. A simple estimation of the effective reflectance of the HR-PhC p-AlGaN contact layer with the Ni/Mg electrode indicated a value exceeding 90%.

AlGaN-based ultraviolet-B (UVB) LEDs at 310 nm emissions are expected to offer safe and smart size UVB-light sources compared to the toxic mercury UV-lamp. Previously, the issue of nonlinearity in the emitted light output power (L) as well as in the external quantum efficiency (EQE) of 310 nm band UVB LEDs were observed. First, the influence of both the number of n-AlGaN buffer layers (BLs) and the type of p-electrodes on the recovery of linear behavior in the L and EQE were investigated. It was found that the nonlinearity in the L and EQE of UVB LED is independent of the number of BLs as well as type of p-electrodes. Therefore, finally the dependence of nonlinearity in the L and EQE on the thickness of quantum-well-barrier (T QWB) of multi-quantum-wells (MQWs) were also considered. Subsequently, the issue of nonlinear behavior in the L and EQE was resolved by the thickness reduction of T QWB from 25 to 10 nm in the MQWs. Similarly, a reasonable value of improvement in both L and EQE, respectively, up to 12 mW and 2.2% of 310nm band UVB LED were realized.

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Aluminium gallium nitride (AlGaN)‐based ultraviolet‐B light‐emitting diodes (UVB LEDs) are expected to offer smart size, wider choice of UVB light emission in the wavelengths range of 280 nm > λ > 320 nm, and low cost as well as low power consumption compared with other UV light sources including toxic mercury UV‐lamps. The hole‐tunneling from p‐AlGaN side of UVB LED into the multi‐quantum‐wells (MQWs) is strongly dependent on the thickness (TFB) and Al‐contents of undoped (ud)‐AlGaN final barrier (FB). Herein, the photoluminescence (PL) efficiency from MQWs of the UVB LED devices is investigated and compared with the electroluminescence (EL) spectra as a function of TFB. Subsequently, the dependence of PL efficiency, external quantum efficiency (EQE), and light output power on the TFB of UVB LEDs is attempted, using the same growth condition for all samples except variation in TFB. When TFB is set to 6–7 nm, improvements in the EQE and light output power, respectively, from 4.3% and 7 mW to the high values of 5.6% and 17 mW in emission band of 295–300 nm under continuous‐wave (cw) at room temperature (RT) are achieved.