Fabrication and Characterizations of Porous AlGaN Distributed Bragg Reflectors with Excellent Thermal Stability at High Temperature

Abstract

Distributed Bragg reflectors (DBRs) made from nanoporous GaN structures are essential for light emitting diodes (LEDs) and vertical cavity surface-emitting lasers, yet they encounter stability challenges at elevated temperature during subsequent growth process. This study addressed these challenges by the usage of multiple pairs of n-AlGaN/u-AlGaN, instead of n-GaN/u-GaN, for the fabrication of lattice-matched DBRs with a technique of electrochemical etching. Our findings from scanning electron microscopy and reflectance spectra indicate that the incorporation of Al promotes the electrochemical etching process and improves the uniformity of porosity. The stop bands of the fabricated porous AlGaN DBRs were centered at around 600 nm with a reflectance of nearly 96%. Additionally, room-temperature Raman spectra were measured for porous AlGaN films annealed for different times to clarify the relationship between residual strain and thermal annealing. The effect of high-temperature annealing on the luminescence properties of the porous AlGaN DBR was investigated by photoluminescence and X-ray photoelectron spectroscopy. The results demonstrated that the incorporation of Al significantly enhanced the thermal stability of the porous DBR structures. As a contrast, we observed decomposition and recrystallization in porous GaN DBRs after high-temperature annealing at 1138 °C with nanoimprinted SiO₂ masks. Our research demonstrates that porous GaN DBRs with a few percent of Al exhibit excellent thermal stability, highlighting their potential for applications in micro-LEDs and other optoelectronic devices.