Strong Lateral Mode Confinement by Embedding SiO2 Nanospheres in the DBRs of GaN-Based VCSELs

In this work, we report the realization of curved distributed Bragg reflectors (DBRs) without the need for lithography to achieve strong lateral confinement in a GaN-based vertical cavity. By embedding SiO2 nanospheres during deposition, curved DBRs with a funnel-shaped cross-section were fabricated. Based on the formed curved DBRs, a vertical cavity with a quality factor exceeding 2800 and a mode volume below 0.14 μm3 was successfully fabricated. The optical pumping threshold power of a vertical cavity surface-emitting laser (VCSEL) with a curved DBR was reduced to 76 nW, which is one order of magnitude lower than that of the same VCSEL with double-planar DBRs. Near-field patterns revealed that the curved-DBR VCSEL emits a circularly symmetric TEM00 mode with a full width at half maximum (FWHM) of only 1.8 μm. We believe this is an effective technique for fabricating low-threshold or small-aperture VCSELs.