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AlGaN LEDs emitting < 230 nm UV light were fabricated on sapphire substrates. We employed a quantum well (QW) with an extremely thin barrier to enhance the quantum confinement of holes, wherein the calculation showed that the topmost valence subband became X ± i Y -like and increased the transverse-electric polarized emission. Additionally, we modified the Al composition of the spacer layer situated between the QW and an electron-blocking layer, which significantly improved the current-injection efficiency. The combination and optimization of these structures produced an LED emission of 228-nm UV light with an output power of 1.4 mW at 150 mA. [ABSTRACT FROM AUTHOR]

Nonradiative recombination (NRR) processes through defect states and their temperature dependence in UV-B AlGaN MQW sample on sapphire substrate grown by MOCVD technique have been studied by photoluminescence (PL) spectroscopy. We detected NRR centers by adding a below-gap excitation light with photon energies from 0.93 eV to 1.46 eV on an above-gap excitation light of 4.66 eV. All the BGE energies decreased PL intensity at 25 K, and the most-distinct quenching is observed by 1.27 eV BGE at the same BGE photon number density. The temperature-dependent PL intensity for the BGE energy of 1.27 eV is interpreted by three NRR centers. The one-level model dominates over that of two-level model in the temperature range 58 K < T < 88 K. The two-level model prevails in other region of temperature. The combination of one-level and two-level models is consistent with the spectral peak-energy shift as a function of temperature. • Investigates NRR processes in UV-B AlGaN MQW by adding below-gap excitation light. • Detects NRR centers by observing PL-intensity change due to below-gap excitation. • Identifies correlation of T -dependent NRR processes with T -dependent PL peak-energy. • Interpret T -dependent NRR processes by a model based on SRH statistics. [ABSTRACT FROM AUTHOR]