Recent progress in GaN-based vertical-cavity surface-emitting lasers with lateral optical confinement due to an incorporated curved mirror

Abstract

The recent progress of GaN-based vertical-cavity surface-emitting lasers (VCSELs) with incorporated curved mirrors at one end of their cavities is reviewed. GaN-VCSELs consisting of 3 InGaN/GaN quantum wells, current apertures formed by boron ion implantation, and curved mirrors at one end of the cavities were fabricated. The near-field and far-field patterns exhibited Gaussian-like profiles, and their divergences agreed well with the theoretical values calculated from the radius of curvature of the curved mirror and the cavity length. The near-field beam waist for a GaNVCSEL with a 6-μm current aperture was as small as 1.4 μm (half width at 1/e2), which indicated that the light was laterally confined by the incorporated curved mirror and that the current aperture could be made smaller than 6 μm. For a GaN-VCSEL with a current aperture of 4μm, a threshold current of as low as 0.56 mA (Jth = 4.5 kA/cm2) was obtained at room temperature under CW operation at a wavelength of 451.8 nm. To the best of our knowledge, this is the lowest threshold current reported among all-dielectric DBR type GaN-VCSELs and is comparable with the lowest value reported for GaN-VCSELs that have a two-dimensional quantum well structure. The authors believe this result to be a milestone for the realization of GaN-VCSELs with extremely low power consumption.