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Developing efficient active region structures with low sensitivity to threading dislocation density (TDD) is of great technical significance for AlGaN-based deep ultraviolet (DUV) light-emitting devices. Here, we propose an active region strategy by introducing bunching effect to form self-assembled sidewall quantum wells (SQWs) with much stronger carrier confinement, resulting in a significant enhancement of internal quantum efficiency (from 46% to 59%) compared to the commonly adopted multiple quantum wells (MQWs) due to the lower sensitivity to TDD. As a demo, an AlGaN-based DUV light-emitting diode (LED) with the proposed active region involving both SQWs and MQWs presents dual-band emission and a consequent 68% enhancement in light output power compared to the DUV-LED with only MQWs as the active region, suggesting that the proposed architecture is fully suitable for the development of high performance DUV light-emitting devices even based on poor or medium quality materials. [ABSTRACT FROM AUTHOR]

Evolution of crystalline quality of AlN via high-temperature (HT) annealing induced by different sapphire pretreatments is investigated. It is found that after HT annealing at 1700 °C for one hour, an AlN film grown on a nitridation treated sapphire substrate presents a much lower threading dislocation density (TDD) than that grown on an alumination treated one, indicating that the combination of nitridation and HT annealing is a more effective approach to achieve high quality AlN. It is verified that the much greater grain density of the nucleation layer induced by nitridation can produce more columns with much smaller sizes so that they can more easily rotate during the HT annealing to reduce the TDD more effectively. A deep ultraviolet light-emitting diode (285 nm) with an output power over 10 mW has been demonstrated on a HT annealed AlN template with sapphire substrate nitridation pretreatment, showing great potential for applications. [ABSTRACT FROM AUTHOR]

AlGaN-based deep-ultraviolet light emitting diodes adopting an embedded delta-AlGaN thin layer with an Al composition higher than that in conventional barriers have been investigated. The experimental result shows that when the current is below 250 mA, the maximum of the external quantum efficiency and light output power for the proposed structure reach severally 1.38% and 10.1 mW, which are enhanced significantly by 160% and 197%, respectively, compared to the conventional ones, showing a tremendous improvement. We attribute that to the inserted delta-thin layer's modulation effect on the energy band, namely, accelerating holes to cross the high barrier with very large kinetic energy, thus increasing the hole injection into the active regions. Meanwhile, the electron concentration within the active regions is enhanced as well because of the accompanying additional effect of the delta-AlGaN thin layer being an electron barrier to block electrons escaping from the active region. [ABSTRACT FROM AUTHOR]