A magnesium delta-doped AlGaN last barrier (MDDLB) was introduced in the structure of deep ultraviolet light emitting diodes (DUV LEDs) to improve their light output power. The MDDLB effectively improved hole injection efficiency and increased the hole concentration at the last AlGaN well of DUV LEDs. It also raised the potential barrier for electron transport from multiple quantum wells to the p-side. Therefore, it reduced overflow of electrons into the p-side of DUV LEDs. These phenomena improved light emitting efficiency of DUV LEDs with the MDDLB. In addition, the current crowding effect was suppressed by the MDDLB in DUV LEDs. Therefore, the 350 mA-light output power of DUV LEDs with the MDDLB was approximately 30% larger than that of DUV LEDs without the MDDLB. Furthermore, the largest light output power of DUV LEDs with the MDDLB was 55 mW, which was approximately 46% larger than that of DUV LEDs without the MDDLB. The suppressed current crowding effect by the MDDLB also reduced efficiency droops of DUV LEDs with the MDDLB. Therefore, efficiency droops of DUV LEDs decreased from 64% to 55% when the MDDLB was introduced.
The p-AlGaN/AlGaN superlattice (SL) hole injection structure was introduced into deep ultraviolet (DUV) light-emitting diodes (LEDs) to enhance their performances. The period thicknesses of the p-Al0.8Ga0.2N/Al0.48Ga0.52N SLs affected the performances of the DUV LEDs. The appropriate period thickness of the p-Al0.8Ga0.2N/Al0.48Ga0.52N SL may enhance the hole injection of DUV LEDs. Therefore, compared with the reference LEDs, the DUV LEDs with the 10-pair Al0.8Ga0.2N (1 nm)/Al0.48Ga0.52N (1 nm) SL presented forward voltage reduction of 0.23 V and light output power improvement of 15% at a current of 350 mA. Furthermore, the 10-pair Al0.8Ga0.2N (1 nm)/Al0.48Ga0.52N (1 nm) SL could slightly suppress the Auger recombination and current overflow of the DUV LEDs in a high-current operation region. In addition to improved carrier injection, the DUV LEDs with the p-Al0.8Ga0.2N/Al0.48Ga0.52N SL hole injection structure showed reduced light absorption at their emission wavelength compared with the reference LEDs. Therefore, the DUV LEDs with p-Al0.8Ga0.2N/Al0.48Ga0.52N SL may exhibit better light extraction efficiency than the reference LEDs. The enhancement of p-Al0.8Ga0.2N (1 nm)/Al0.48Ga0.52N (1 nm) SL may contribute to improvements in light extraction and hole injection.
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