Effect of Wet Etching on AlGaN-Based Ultraviolet-B Laser Diodes Grown on Wet-Etched Periodic AlN Nanopillars

The effect of wet etching on the characteristics of ultraviolet-B (UV-B) lasers fabricated on AlGaN templates grown as crystals or wet-etched AlN nanopillars is compared in detail. Specifically, a tetramethylammonium hydroxide (TMAH) solution is used to form templates with AlN nanopillars of different diameters, followed by determining the dependence of the dislocation density in AlGaN crystals grown on the templates, the threshold power density (Pth) of an optically pumped UV-B laser, and the threshold current density (Jth) of a UV-B laser diode (LD) on the extent of etching. It is observed that the pillar diameter decreases almost linearly as the etching time with the TMAH solution increases. The dislocation density of AlGaN crystals grown on AlGaN templates is almost independent of the etching time. Meanwhile, Pth of the optically pumped UV-B laser is almost halved upon etching with TMAH. Finally, the Jth of the UV-B LD tends to decrease by 10%-20% upon etching. The optical gain is estimated by optical excitation; wet etching of AlN nanopillars with TMAH solution results in a larger optical gain at the same excitation intensity, indicating that nonradiative recombination centers, such as point defects, are reduced. Herein, characteristics of ultraviolet B lasers fabricated on AlGaN templates grown on AlN nanopillars treated with tetramethylammonium hydroxide aqueous solution are discussed. The threshold of the laser is clearly reduced compared to the nontreated case. No change in dislocation density is observed with the treatment, suggesting other effects such as point defect reduction.image (c) 2024 WILEY-VCH GmbH