Milliwatt-class GaN-based blue vertical-cavity surface-emitting lasers fabricated by epitaxial lateral overgrowth

TLDR: In this paper, a 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 was achieved.

Abstract: 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.