GaN/AlGaN ultraviolet light-emitting diode with an embedded porous-AlGaN distributed Bragg reflector

Abstract

A GaN/AlGaN-based ultraviolet light-emitting diode (LED) structure with an embedded porous-AlGaN reflector was fabricated by a doping-selective electrochemical (EC) wet-etching process. The n+-AlGaN/undoped-AlGaN (u-AlGaN) stack structures with different Al contents were transformed into porous-AlGaN/u-AlGaN stack structures that acted as the embedded distributed Bragg reflectors (DBRs). The porosity of the EC-treated AlGaN layer was increased by decreasing the Al content in the n+-AlGaN layer. The reflectivity of the porous-AlGaN DBR structure was measured to be 90% at 379.3 nm with a 37.2 nm stopband width. The photoluminescence emission intensity of the DBR-LED was enhanced by forming the embedded porous-AlGaN DBR structure.

Porous AlGaN-Based Ultraviolet Distributed Bragg Reflectors

“…This process uses an electrochemical etching (ECE) process to create pores in subsurface doped GaN without significant damage to the non-intentionally doped (NID) GaN layers. Porous AlGaN DBRs with 90% reflectivity at 379.3 nm have been demonstrated to enhance the photoluminescence of LEDs [ 7 ], and they have significantly enhanced the electroluminescence of GaN LEDs around 360 nm [ 8 ]. Both of these demonstrations required laser scribed access trenches to be patterned in order to create subsurface porosity, which increases the complexity and the cost of device production.…”

Review of nanophotonics approaches using nanostructures and nanofabrication for III-nitrides ultraviolet-photonic devices

“…DBRs have been used as high reflective mirrors in many UV-based photonic devices (summarized in Table 5), e.g., vertical-cavity surface-emitting laser (VCSEL), [129][130][131] edge-emitting laser (EEL), 139 microdisk LD, 137 resonant-cavity LED (RCLED), 132 resonant-cavity PD (RCPD), 133 and LEDs. 70,[134][135][136]138 These DBRs were formed using oxides named as UV-dielectric DBR and group III-nitride semiconductors, named as UV-nitride DBR. Most of the aforementioned UVbased photonic devices require DBR(s) with high reflectivity, R > 99%.…”

“…To overcome limitations, epitaxially grown UV-nitride DBRs have been developed using lattice-mismatched material [(Al)GaN/Al(Ga)N-based, e.g., GaN/AlN, 146 GaN/AlGaN, [147][148][149][150] AlGaN/AlGaN, 151 AlGaN/ AlN, [152][153][154] and boron-containing nitride, i.e., BAlN/AlN 155 ], lattice-matched material (AlInN/AlGaN), [156][157][158][159] and nitride-porous (AlGaN/air) material. 135 The advantage of the UVnitride DBRs is that they can be monolithically grown and doped (either por n-doped for electrical pumping), and they are furthermore thermally conductive. However, obtaining crack-free DBRs is challenging due to the limitation in crystal growth (substrate compatibility, i.e., latticeand thermal expansion-mismatch, and accumulation of tensile stress) and inadequate RI contrast, i.e., higher periods are required which is challenging for crystal growth in addition to the narrow DBR stopband.…”

Performance-Enhanced 365 nm UV LEDs with Electrochemically Etched Nanoporous AlGaN Distributed Bragg Reflectors

“…The electrochemically-etched u-GaN/n + -GaN stack structures have a high refractive index contrast and perfectly matched lattice constant, and high reflectance (>99%) can be obtained in the visible band. Porous AlGaN DBRs have also been reported [19,20] recently in the near UV band, and high reflectance of 90% (at 379 nm) and 93% (at 374 nm) have been obtained, respectively. Yet, almost all the optoelectronic devices based on the porous (Al)GaN DBRs could only be applied in optically pumped conditions so far, because the n-type layers and active regions could also be etched by the electrolytes inevitably, and thus would result in the increase of series resistance and decrease of internal efficiency.…”