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In this work, by sandwiching a p-AlGaN layer into the n-AlGaN layer, we generate an energy barrier in the n-AlGaN layer to improve the current spreading effect of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). The abrupt energy barrier can balance the resistivity in the n-AlGaN layer, and this leads to the better lateral current distribution in the p-type hole injection layer. Numerical and experimental results show that the homogenized current distribution enables the enhanced external quantum efficiency (EQE) for the proposed DUV LED. In addition, the better conductivity modulation arising from the more homogenized current distribution decreases the forward voltage and suppresses the self-heating effect. [ABSTRACT FROM AUTHOR]

Tuning the plasmonic resonance peak to the deep ultraviolet (DUV) band is critical for plasmonic-enhanced AlGaN-based DUV photodetector. However,the high refractive index of AlGaN layer seriously limits the plasmonic resonance peak in DUV band. Therefore, in this work, we study how various Al nanoparticles on the AlGaN layer surface affect the plasmonic resonance performance. Compared with the Al-based nanosphere, nanohemisphere and nanodisk, the Al-based nanorod is the most suitable candidate for AlGaN-based DUV photodetectors. This is because the DUV plasmonic dipolar mode excited from the upper part of nanorod is not affected by the interface between the nanorods and the AlGaN layer. However, the interface also leads to another plasmonic dipolar mode at longer wavelengths. Moreover, the DUV plasmonic resonance peak will be influenced by the diameter, the height and the Al2O3 layer thickness. We also find that the diffraction can enhance the resonance peak intensity when the Al nanorod period is smaller than the resonance peak wavelength. Besides, to make the enhanced electric field located in active layer, a layer of Ga2O3 shell is proposed to cover Al nanorods, which causes a quadrupole mode in DUV band excited from the sidewall of Al nanorods. [ABSTRACT FROM AUTHOR]

We experimentally and numerically propose a deep ultraviolet light-emitting diode (DUV LED) possessing the quantum barriers (QBs) with the gradually reduced Al composition along the [0001] orientation. The induced negative polarization bulk charges in the graded QBs can screen the positive polarization sheet charges at the QB/quantum well (QW) interface, i.e., generating the polarization self-screening effect, which weakens the electric field in the QWs. The polarization self-screened feature is important in enhancing the overlap level of the electron and hole wave functions within the active region and increasing the hole injection, thus improving the electroluminescence intensity and the optical power. [ABSTRACT FROM AUTHOR]

In this work, and experimentally propose inserting an SiO2 intermediate layer between the Ti and n-AlGaN layer to improve the electron injection efficiency. When the SiO2 intermediate layer is adopted, the SiO2 layer can share a part of the applied voltage and then weakens the surface depletion effect, which is confirmed by the capacitance–voltage measurement. Furthermore, the energy bending of the SiO2 layer pushes the affinity of Ti to be even higher than the conduction band of the Al0.60Ga0.40N layer, which then screens the Schottky barrier and favors the election injection. The influence of the thickness of the SiO2 intermediate layer is also investigated in this work. When the SiO2 layer becomes thick, the tunneling capability of the electrons will be significantly limited due to the increased tunnel region width, leading to increased forward voltage. [ABSTRACT FROM AUTHOR]

Current crowding effect for AlGaN based ultraviolet-B light-emitting diodes (UVB LEDs) is normally observed at high injection current levels, which can cause non-uniform optical emission and generate very high local heat. In this work, UVB LED with a PNP-AlGaN current spreading layer is fabricated and studied. The PNP-AlGaN current spreading layer is obtained by sandwiching the n-AlGaN layer into the p-AlGaN layer. Owing to the modulated energy band profiles by the different doing types, the formed energy barriers for holes in PNP-AlGaN layer can make the current more uniformly distributed laterally and therefore the hole injection efficiency at the mesa edges can be enhanced. As a result, the measured external quantum efficiency (EQE) and optical output power for the proposed UVB LED is increased. Moreover, thanks to the enhanced current spreading effect, the thermal droop for the optical output power is suppressed and the forward voltage decreases for the proposed architecture. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the origin of efficiency droop for AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). We find that the efficiency droop is likely to be caused by the electron leakage for DUV LEDs studied in this work. The electron leakage arises from the unbalanced electron and hole injection efficiencies. The correlation between the efficiency droop and the electron leakage can be numerically calculated by manipulating the conduction band barrier height of the p-AlGaN electron blocking layer (p-EBL) for the proposed DUV LEDs. For the purpose of demonstrating that the efficiency droop for DUV LEDs can be experimentally decreased by reducing the electron leakage, a p+-GaN/In0.15Ga0.85N/n+-GaN tunnel junction on DUV LED is grown by using metal organic chemical vapor deposition (MOCVD) technology. The tunnel junction helps to enhance the hole injection, thus decreasing the electron leakage and the efficiency droop. Moreover, the parasitic emission in the p-type hole injection layer is no longer observed thanks to the decreased electron leakage level. [ABSTRACT FROM AUTHOR]

Low external quantum efficiency of deep ultraviolet light-emitting diodes (DUV LEDs) and current crowding can result in considerable heat generation, which has a great negative impact on device performance. In this paper, we investigate the influence of different electrode patterns on the photoelectric and thermal performance of DUV LEDs. We find that different electrode designs can achieve drastically different optical powers, with the superior design being the n-type electrode surrounding the active region. Moreover, compared with the counterpart, the superior design does not affect the electrical performance. The main reason is that the N-surrounding electrode pattern can provide enough current paths for carrier transport, thus realizing a more uniform current injection and can further improve the external quantum efficiency for DUV LEDs. [ABSTRACT FROM AUTHOR]

In this work, we investigate the effect of sidewall angle, height and space of an air cavity extractor (AC-Extractor) on the polarization-dependent light extraction efficiency (LEE) for AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) using three-dimensional finite difference time-domain method. Compared to the reported inclined sidewall metal reflector (SM-Reflector), DUV LED with AC-Extractor shows better light extraction at any height and inclined angle due to different light extraction mechanisms. The light in SM-Reflector DUV LED is extracted mainly through mirror reflection. However, total internal reflection from the sidewall dominants the contribution to LEE for the AC-Extractor with smaller inclined angle such that the space has little impact, while Fresnel scattering is more important for the AC-Extractor with larger inclined angle and that the additional out-light channel as well as the space play a critical role in enhancing the LEE. And the analysis is further developed into a three-escape-cones analytic model theory. In particular, the AC-Extractor with vertical sidewall is more beneficial to enhance the LEE of DUV LED than that with inclined sidewall, which can be rationally explained based on the three-escape-cones analytic model. [ABSTRACT FROM AUTHOR]

In this paper, a structure of super-lattice structure last barrier (SLSLB) is proposed, which can be applied into the AlGaN-based ultraviolet light-emitting diodes (LEDs) for improving the injection of both electrons and holes. Several other SLSLBs are also designed and compared in this work, and according to the simulated results, we find that the LED with SLSLB of diminishing thickness (SLSLB-D) possesses the highest internal quantum efficiency and the smallest efficiency droop. The SLSLB-D can effectively reduce the electron concentration at the interface between the last barrier (LB) and electron block layer (EBL), which relieves the leakage of electrons. Moreover, the best hole injection capability for the LED with SLSLB-D also contributes to the improved optical performance. [ABSTRACT FROM AUTHOR]

This work reports a nearly efficiency-droop-free AlGaN-based deep ultraviolet light-emitting diode (DUV LED) emitting in the peak wavelength of 270 nm. The DUV LED utilizes a specifically designed superlattice p-type electron blocking layer (p-EBL). The superlattice p-EBL enables a high hole concentration in the p-EBL which correspondingly increases the hole injection efficiency into the multiple quantum wells (MQWs). The enhanced hole concentration within the MQW region can more efficiently recombine with electrons in the way of favoring the radiative recombination, leading to a reduced electron leakage current level. As a result, the external quantum efficiency for the proposed DUV LED structure is increased by 100% and the nearly efficiency-droop-free DUV LED structure is obtained experimentally. [ABSTRACT FROM AUTHOR]

This work proposes the [0001] oriented AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED) possessing a specifically designed p-electron blocking layer (p-EBL) to achieve the high internal quantum efficiency. Both electrons and holes can be efficiently injected into the active region by adopting the Al 0.60 Ga 0.40 N/Al 0.50 Ga 0.50 N/Al 0.60 Ga 0.40 N structured p-EBL, in which a p-Al 0.50 Ga 0.50 N layer is embedded into the p-EBL. Moreover, the impact of different thicknesses for the p-Al 0.50 Ga 0.50 N insertion layer on the hole and electron injections has also been investigated. Compared with the DUV LED with the bulk p-Al 0.60 Ga 0.40 N as the EBL, the proposed LED architectures improve the light output power if the thickness of the p-Al 0.50 Ga 0.50 N insertion layer is properly designed. [ABSTRACT FROM AUTHOR]