In order to achieve high quantum efficiency of AlGaN-based deep ultraviolet light-emitting diodes (UVC-LED), it is important to improve the light extraction efficiency (LEE). In this paper, theoretical simulation and experiment of SiO2 anti-reflective film deposited on UVC-LED were investigated. The effect of different SiO2 thickness on the light extraction efficiency of 275 nm UVC-LED was studied, showing that 140 nm SiO2 anti-reflective film can effectively improve the light output power of UVC-LED by more than 5.5%, which were also confirmed by the TFCALC simulation. The enhancement of UVC-LED light extraction efficiency by this antireflective film is mainly due to the 3λ2 light coherent effect at the SiO2/Al2O3 interface. Our work proved the promising application of antireflective coating on UVC-LED.
The internal-roughed sapphire in a 275-nm AlGaN-based deep-ultraviolet (DUV) LED is fabricated using a laser stealth dicing technique to improve the high-angle extraction. Furthermore, the low-angle extraction is enhanced by depositing a SiO2-antireflection film on the internal-roughed sapphire surface. Compared with conventional DUV LEDs with a light output power (LOP) of 33.05 mW at 350 mA, the LOP of DUV LEDs with internal-roughed sapphire and SiO2-antireflection film increases by 20.85% to 39.94 mW. In addition, combined with finite-difference time-domain simulations, the effect of internal-roughed sapphire on the transmission and light extraction efficiency (LEE) of the DUV LEDs is revealed. The combination of the internal-roughed sapphire substrate and SiO2-antireflection film improves the LEEs of transverse electric (TE) and transverse magnetic (TM) polarized light by 1.6% and 108%, respectively. These results offer the potential for large-scale, low-cost industrial production of high-efficiency DUV LEDs.
The distribution of electrons and holes inside the multiple-quantum wells is highly non-uniform for AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) due to both insufficient hole injection and excessive electron leakage. A key factor to improve the quantum efficiency of DUV-LED is to reduce the proportion of hot electrons in n-AlGaN through carrier deceleration. In this work, we propose a structure design by introducing an additional Al0.55Ga0.45N/Al0.42Ga0.58N superlattice electron restriction layer between the active region and n-AlGaN for electron deceleration. The superlattice structure not only reduces the mobility of the electrons, which helps to balance the distribution of carriers in the active region, thus, promoting radiative recombination, but also facilitates the lateral transport of the electrons, thus, reducing the current crowding effect through band engineering. Low temperature electroluminescence analysis reveals that the improvement of quantum efficiency is due to both enhanced carrier injection efficiency and radiation recombination efficiency in the active region.
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