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.

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 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.

In this research, watt-class green and blue laser diodes, which are fabricated on free-standing semipolar 20 21g f GaN and conventional c-plane GaN substrates, respectively are developed. Although several research groups have recently developed green laser diodes on semipolar GaN substrates, which have weaker piezoelectric fields and higher indium homogeneity in InGaN active regions compared to c-plane GaN, watt-level output power has yet to be achieved. By utilizing the 20 21g f plane, the first watt-class green lasers at 530 nm is successfully fabricated, and achieve maximum output powers in excess of 2 W, which to the best of our knowledge is the highest value reported for any GaN-based green laser diode. A wall-plug efficiency of 17.5% is realized at a current of 1.2 A under continuous-wave operation, which corresponds to an optical output of approximately 1 W and is the highest value reported to date. In addition, high-power and high-efficiency blue laser diodes at 465 nm are successfully fabricated on conventional c-plane GaN substrates. The output power and wall-plug efficiency are 5.2 W and 37.0%, respectively, at a current of 3.0 A under continuous-wave operation. These laser diodes are promising light sources meeting the ITU-R Recommendation BT.2020 for future laser display applications.

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.

True green GaInN laser diodes with a lasing wavelength above 525 nm under continuous wave operation have been successfully fabricated on semipolar {2021} GaN substrates by improving both the diode structure and epitaxial growth conditions. At a case temperature of 55 °C, their lifetime was estimated to be over 5000 h for an optical output power of 50 mW and over 2000 h at 70 mW.

This paper reviews past research and the current state-of-the-art concerning gallium nitride-based vertical-cavity surface-emitting lasers (GaN-VCSELs) incorporating distributed Bragg reflectors (DBRs). This paper reviews structures developed during the early stages of research into these devices, covering both major categories of GaN-based VCSELs: hybrid-DBR and all-dielectric-DBR. Although both types exhibited satisfactory performance during continuous-wave (CW) operation in conjunction with current injection as early as 2008, GaN-VCSELs have not yet been mass produced for several reasons. These include the difficulty in controlling the thicknesses of nitride semiconductor layers in hybrid-DBR type devices and issues related to the cavity dimensions in all-dielectric-DBR units. Two novel all-dielectric GaN-based VCSEL concepts based on different structures are examined herein. In one, the device incorporates dielectric DBRs at both ends of the cavity, with one DBR embedded in n-type GaN grown using the epitaxial lateral overgrowth technique. The other concept incorporates a curved mirror fabricated on (000-1) GaN. Both designs are intended to mitigate challenges regarding industrial-scale processing that are related to the difficulty in controlling the cavity length, which have thus far prevented practical applications of all-dielectric GaN-based VCSELs.

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