Tripling the light extraction efficiency of a deep ultraviolet LED using a nanostructured p-contact

Abstract

Despite a wide array of applications, deep ultra-violet light emitting diodes offer relatively poor efficiencies compared to their optical counterparts. A contributing factor is the lower light extraction efficiency due to both highly absorbing p-contacts and total internal reflection. Here, we propose a structure consisting of a hexagonal periodic array of cylindrical nanoholes in the multi-layered p-contact which are filled with platinum. This nanostructure reduces the absorption of the p-contact layer, leading to a higher emission into the n-contact compared to a planar reference. An optimum geometry of the nanostructure allows a light extraction efficiency of 15.0%, much higher than the typical 4.6% of a planar reference. While the nanostructure strongly decreases the light absorption in the p-contact, it is still not able to considerably reduce the total internal reflection. Consequently, the nanostructured p-contact should be combined with other optical strategies, such as nanopatterned sapphire substrates to increase the efficiency even further. Despite this, the nanostructure described in this work provides a readily realizable path to enhancing the light extraction efficiency of state-of-the-art deep ultra-violet light emitting diodes.

A scattered volume emitter micropixel architecture for ultraefficient light extraction from DUV LEDs

“…Details of this large sapphire LED chip reference calculation can be found in the supporting information. With such a large chip architecture, one obtains an LEE of 4.8% for the "Reference" epi stack case (larger than the 4.6% reported by López-Fraguas et al's semi-infinite planar calculations 38 due to some light escaping through the sapphire sidewalls in our simulations). For the "Low MQW RI" and "Low P-side Loss" epi stack cases, the large chip architecture provides LEE values of 6.5% and 5.4%, respectively.…”

“…7. We consider a simplified monochromatic emission at a wavelength of 265 nm, as performed by López-Fraguas et al 38 . The "Low P-side Loss" epi stack case exhibits a considerably stronger peak close to 80 degrees that is not observed in the other two cases.…”

“…Furthermore, various methods in designing the chip have been studied, including improving the LEE by utilizing micro/nanopatterning on specific layers, where this patterning provides a high probability of surface extraction. Khizar et al enhanced the output power by 55% using microlenses on a sapphire substrate 33 , Zhou et al increased the light extraction gain by 2.5 times by controlled roughening of the AlGaN layer's nitrogen face 34 , Zhao et al improved the LEE by 7.3 times, reaching 12% by patterning microdomes on p-epilayers 35 , Lee et al presented a 67% output power enhancement by injecting air voids in a patterned sapphire substrate (PSS) 36 , Zheng et al achieved an approximately 18% LEE by nanomeshing the pcontact 37 , and López-Fraguas et al tripled the LEE, reaching 12% by nanostructuring the p-contact metal 38 .…”

Integrated metasurfaces for advanced solid-state-lighting

“…The following structures tackle the problem at the source by influencing the spontaneous radiation of the MQWs typically in near proximity to the mirror reflector deposited on the p-doped GaN layer surface. Unlike other recent studies [12], this is achieved with the prerequisite of preventing epitaxial layer etching and the consequent risk of active region damage and/or deterioration of the emitter performance (e.g. reliability, non-radiative channels, etc.…”

Tunable Emission Enhancement in Surface Plasmon‐Enhanced GaN Light‐Emitting Diode Based on the Ag–SiO2 (Ag‐Rich) Cermet Material

“…In recent years, a large number of new technologies about LED have emerged. [55][56][57][58][59][60] If the technology is combined with those new technologies such as Tamm plasmon cavity, [3] quasiperiodic gratings, [55] localized surface plasmon induced on surface silver gratings, [56] nanopatterned sapphire substrates, [57] localized surface plasmon induced by Ag/p-GaN double grating, [58] nanostructured p-contact, [59] asymmetric In x Ga 1-x N/InN double QWs, [60] and so on they are expected to further improve η ext of GaN LEDs with cyan and green bands.…”