Developments of blue-violet laser-diode structures suitable for mass production (RiS-LD)

摘要

We have developed novel ridge-type blue-violet laser diodes fabricated by selective re-growth on GaN substrates (RiS-LD). In this paper, we focus on key issues concerning the ridge by selective re-growth in the LDs, and report the improvement of laser characteristics based on detailed analyses of these issues. First, we investigate the compositional modulation in AlGaN-alloy selective growth by systematical experiments, and clarify the mechanism. This enables us to control precisely Al mole fraction of p-AlGaN cladding layers in the ridges, and we have successfully realized a superior beam profile with the lowest aspect ratio of 2.0. Second, we verify the internal loss of RiS-LDs mainly originates from absorption in the re-growth boundary and Mg-doped GaN layer. To avoid these absorptive regions, we shift the perpendicular optical field to n-cladding side. This reduces the loss significantly, and a low threshold current of 10 mA has been obtained. These superior characteristics are owing to the fabrication method of the LDs, which combines epitaxial growth on high-quality GaN substrates with the ridge formation using selective-growth technique.