Green VCSELs based on nitride semiconductors

Vertical-cavity surface-emitting lasers (VCSELs) are promising in various applications including full-color mobile projectors, laser precision processing, display, armarium and high-speed air-water optical wireless communication systems with a unique combination of advantages. However, GaN-based VCSELs with emission wavelengths in green are challenging because of the low emission efficiency of green emitting InGaN QWs. This is known as the green gap, which is mainly caused by the quantum-confined Stark effect and the high density of defects and dislocations. In this paper, we would like to discuss the origin of the green gap and possible approaches to overcome it, and then review our recent progress in green VCSELs: (1) lasing from 479.6 to 565.7 nm by using QD active area; (2) lasing at 545 nm by using QD-in-QW active structure; (3) lasing at 493 nm by utilizing blue-emitting InGaN QWs with the combination of cavity effect. (C) 2020 The Japan Society of Applied Physics.