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We report a narrow divergence angle in a blue gallium-nitride-based visible vertical-cavity surface-emitting laser (GaN-VCSEL) with a curved mirror. This device exhibited continuous-wave operation at a wavelength of 447.9 nm. The full-width at half-maximum divergence angle of the 8 &#x03BC;m-aperture VCSEL was 3.9&#x00B0; when the device was operated at a current of 1.2 &#x00D7; Ith, where Ith is the threshold current. In this type of cavity, the radius of curvature (ROC) of the curved mirror determines the near-field pattern (NPF) and far-field pattern (FFP). The authors fabricated devices having ROC up to 988 &#x03BC;m, which is more than 10 times greater than the ROC of the mirror used in the previously reported structures, allowing this narrow emission. The I&#x2013;L characteristics showed that the Ith value increased with increasing ROC. The present study investigates the mechanism behind this tendency in detail.

Narrow Emission of Blue GaN-Based Vertical-Cavity Surface-Emitting Lasers With a Curved Mirror