Deep-UV Porous AlGaN Distributed Bragg Reflectors for Deep Ultraviolet Light-Emitting Diodes and Laser Diodes

Abstract

A porous-Al0.47GaN/n-Al0.47GaN stack structure with a large refractive index contrast has been fabricated through a homoepitaxial growth process on a Si-doped n+-Al0.47GaN/n-Al0.47GaN stack structure with a simple electrochemical wet etching process. A 20-pairs porous-Al0.47GaN distributed Bragg reflector structure (DBR) with a high aluminum content was fabricated at the deep-ultraviolet wavelength region of light emitting diodes. Low compressive strain and high reflectance has been observed in a porous-AlGaN/n-AlGaN DBR structure with 93% reflectivity at 276 nm. The high reflectance spectrum was measured at the 265 to 287 nm wavelength region in the porous AlGaN DBR structure. The absorption wavelength of the AlGaN layer was observed at about 250 nm, which is shorter than the high reflectance wavelength region of the porous DBR. Light extraction efficiency of the deep-UV optoelectronic devices can be improved by integrating the embedded porous AlGaN reflectors during the epitaxial growth process.

Ultraviolet-C AlGaN Resonant-Cavity Light-Emitting Diodes with Thermal Stability Pipe-AlGaN-Distributed Bragg Reflectors

“…The n + -AlGaN:Si epitaxial layer with a high refractive index can be transformed into the conductive porous AlGaN:Si layer with a low refractive index through an electrochemical (EC) wet etched process. EC-treated porous AlGaN/AlGaN DBR had been demonstrated as a reflector in our previous report …”

“…EC-treated porous AlGaN/AlGaN DBR had been demonstrated as a reflector in our previous report. 19 In this paper, the AlGaN-based UVC resonant-cavity LED (RC-LED) structures with top and bottom pipe-AlGaN distributed Bragg reflectors (DBRs) have been fabricated. For the top/bottom pipe-AlGaN DBR structures, 20 pairs of the epitaxial n + -AlGaN:Si/n-AlGaN:Si stack structures were transformed into the pipe-AlGaN/n-AlGaN DBR structures through a doping-selective EC wet etching process.…”

Nanoporous AlGaN Distributed Bragg Reflectors for Deep Ultraviolet Emission

“…24 Recently, Wu et al have reported the lateral electrochemically etched n + -Al 0.47 Ga 0.53 N/n-Al 0.47 Ga 0.53 N DUV NP-DBRs with 93% reflectance at 276 nm. 25 The N d of the n + -Al 0.47 GaN and n-Al 0.47 GaN layers were 2 × 10 19 and 5 × 10 18 cm −3 , respectively. Although lateral EC etching is more favorable to achieve high porosity, separated mesas that are tens to hundreds of μm wide are disadvantageous for fabricating large-scale DBRs and related devices.…”

“…Few studies have reported reflectance close to 90%, but with Al content not exceeding 15% , and stopband staying at near UV . Recently, Wu et al have reported the lateral electrochemically etched n + -Al 0.47 Ga 0.53 N/ n -Al 0.47 Ga 0.53 N DUV NP-DBRs with 93% reflectance at 276 nm . The N d of the n + -Al 0.47 GaN and n -Al 0.47 GaN layers were 2 × 10 19 and 5 × 10 18 cm –3 , respectively.…”

Fabrication of wafer-scale nanoporous AlGaN-based deep ultraviolet distributed Bragg reflectors via one-step selective wet etching

“…As the n-doped AlGaN is selectively etched into porous morphology, a large refractive index contrast is formed between n-doped and undoped layers, and same Al content avoids lattice and thermal mismatch 11 . At present, laterally ECE and vertically-laterally ECE are the two main methods for preparing nanoporous (NP)-DBRs 12,13 . Using these two methods, GaN-based NP-DBRs have been widely reported in the blue and near-ultraviolet spectral regions [14][15][16][17] .…”