Nanoporous AlGaN Distributed Bragg Reflectors for Deep Ultraviolet Emission

In this paper, we demonstrated wafer-scale AlGaN-based deep ultraviolet (DUV) nanoporous (NP) distributed Bragg reflectors (DBRs) by vertical electrochemical (EC) etching. The stopbands of the NP-DBRs were centered around 280 nm with reflectance close to 90%. A thick AlGaN film and four-period multiple quantum wells (MQWs) were grown on the strain-relaxed NP-DBRs template. The reciprocal space mappings (RSMs) revealed the increased compressive strain in MQWs grown on NP-DBRs, and transverse electric (TE) mode emission was enhanced due to this strain modulation. Thanks to the reflection effect, the photoluminescence (PL) intensity of the MQWs in the NP-DBR region was more than twice that of the region without NP-DBRs. The anisotropic optical polarization measurements and theoretical simulations demonstrated that the light extraction of both TE and transverse magnetic (TM) modes were improved by reflection, and the sideward light can be deflected upward by scattering by the etched nanovoids. Especially, the TM mode light was more extracted by NP-DBRs. Our work highlighted the possible applications enabled by the DUV NP-DBRs in light reflection and structural reconstructions of AlGaN-based UV emitters.