We demonstrate the lateral optical confinement of GaN-based vertical-cavity surface-emitting lasers (GaN-VCSELs) with a cavity containing a curved mirror that is formed monolithically on a GaN wafer. The output wavelength of the devices is 441–455 nm. The threshold current is 40 mA (Jth = 141 kA/cm2) under pulsed current injection (Wp = 100 ns; duty = 0.2%) at room temperature. We confirm the lateral optical confinement by recording near-field images and investigating the dependence of threshold current on aperture size. The beam profile can be fitted with a Gaussian having a theoretical standard deviation of σ = 0.723 µm, which is significantly smaller than previously reported values for GaN-VCSELs with plane mirrors. Lateral optical confinement with this structure theoretically allows aperture miniaturization to the diffraction limit, resulting in threshold currents far lower than sub-milliamperes. The proposed structure enabled GaN-based VCSELs to be constructed with cavities as long as 28.3 µm, which greatly simplifies the fabrication process owing to longitudinal mode spacings of less than a few nanometers and should help the implementation of these devices in practice.

Continuous-wave operation of InGaN green laser diodes (LDs) on semipolar f2021g GaN substrates with output powers of over 100 mW in the spectral region beyond 530 nm is demonstrated. Wall plug efficiencies (WPEs) as high as 7.0-8.9% are realized in the wavelength range of 525-532 nm, which exceed those reported for c-plane LDs. The longest lasing wavelength has reached 536.6 nm under cw operation. These results suggest that the InGaN green LDs on the f20 21g plane are better suited as light sources for applications requiring wavelengths over 525 nm.

We have achieved continuous‐wave (CW) operation of gallium nitride (GaN)‐based vertical‐cavity surface‐emitting lasers (VCSELs) fabricated by epitaxial lateral overgrowth (ELO) using dielectric distributed Bragg reflectors (DBRs) as masks for selective growth. The GaN VCSELs exhibited CW operation at a wavelength of 453.9 nm, and the maximum output power was 1.1 mW, which is the highest value reported to date. GaN‐based materials have presented challenges for obtaining DBRs with high reflectivity and a wide stopband, precise control of the cavity length and a lateral confinement structure to provide laser operation. The proposed VCSEL is immune to these concerns. Its two dielectric DBRs were obtained free from cracks. A high reflectance of more than 99.9% and a stopband with a width of 80–97 nm were obtained for both DBRs. The cavity length was controlled by epitaxial growth to as short as 4.5 µm. An ITO contact electrode on p‐type GaN, which is required for a lateral confinement structure, showed electrical reliability under a high current density of 59.6 kA cm−2. The present data demonstrate that the fabrication process adopted here overcomes the shortcomings that have prevented the widespread use of GaN‐based VCSELs.

We have successfully demonstrated the room-temperature continuous-wave operation of GaN-based vertical-cavity surface-emitting lasers (VCSELs) with all-dielectric reflectors, which were fabricated using epitaxial lateral overgrowth. The VCSELs exhibited a threshold current of 8 mA and a threshold voltage of 4.5 V at a lasing wavelength of 446 nm. The maximum output power was 0.9 mW for an 8-µm-diameter current aperture, which was made possible because of the high thermal conductivity of the GaN substrate.

Boron ion implantation, which is used for confining carriers in gallium nitride (GaN)-based vertical-cavity surface-emitting laser diodes (VCSELs), was studied. Detailed analysis indicated that boron ion implantation of GaN increases GaN’s absorption coefficient from zero to 800 cm−1 and its refractive index from 2.45 to 2.51 at the surface of the wafer at a wavelength of 453 nm. The depth profile of boron obtained by secondary ion mass spectroscopy (SIMS) showed an exponential decrease toward the bottom of the wafer. Assuming that the changes in optical parameters caused by implantation are proportional to the concentration of boron in GaN, the boron ion implantation applied to GaN-VCSELs causes optical absorption of 0.04% per round trip in the cavity and extends the light path of the cavity by 2.2 nm, both of which apparently have negligible impact on the operation of GaN-VCSELs. The implanted boron ions pass through the active regions, introducing non-radiative recombination centers at the edges of those active regions made of InGaN multi-quantum wells, which, however, does not cause significant current injection loss.

This review introduces the latest progress on gallium nitride (GaN)-based visible vertical-cavity surface-emitting lasers (VCSELs) with features such as plane and curved distributed Bragg reflectors (DBRs) made of dielectric materials and boron ion implantation to form current apertures. This novel class of GaN-based VCSELs allow small apertures down to 3 μm and long cavities of more than 20 μm without the occurrence of diffraction loss. These structures have enabled low threshold currents (e.g., I th = 0.25 mA), high efficiency operation (e.g., WPE = 9.5%), and robust fabrication processes with high lasing yield. All those characteristics are the best among those previously reported GaN-based VCSELs. The proposed structure should facilitate the production of VCSELs formed on semi-polar plane GaN substrates and arrayed VCSELs, which are expected to realize novel light emitters that have been previously difficult to fabricate, such as green VCSELs and watt-class blue VCSEL arrays.

The continuous wave operation of a gallium-nitride-based vertical-cavity surface-emitting laser (GaN-based VCSEL) that uses boron ion implantation for lateral current confinement and a curved mirror for lateral optical confinement was investigated. The threshold current was 0.25 mA (Jth = 3.5 kA cm−2) for a 3 μm diameter current aperture at room temperature and the lasing wavelength was 445.3 nm. This is the lowest threshold current recorded for a GaN-based VCSEL. This result is considered to be a milestone for the further miniaturization of GaN-based VCSELs by the implementation of lateral optical confinement due to the incorporation of a curved mirror.

We report single transverse mode operation of a blue GaN-based vertical-cavity surface-emitting laser (GaN-VCSEL) with a monolithically incorporated curved mirror. For a device with a 4 μm current aperture diameter and a curved mirror with a radius of curvature (ROC) of 51 μm, single transverse mode operation was confirmed up to an output power of 3.2 mW under continuous wave operation at 20 °C. For a device with a smaller ROC of 31 μm, multi transverse mode operation was confirmed, indicating that the transverse mode can be controlled by the cavity design of such GaN-VCSELs.