Continuous Wave Operation of GaN Vertical Cavity Surface Emitting Lasers at Room Temperature

We report on continuous wave lasing characteristics of GaN vertical cavity surface emitting lasers (VCSELs). The VCSEL operates at room temperature under current injection by using highly reflective distributed Bragg reflectors (DBRs) made up of transparent ${\rm ZrO}_{2}$ and ${\rm SiO}_{2}$ film stacks. Together with high reflectivity and the wide stop band of the DBR, the long cavity of 6 $\mu{\rm m}$ allows multimode lasing oscillation with narrow mode spacing of 2.9 nm. In addition, a short cavity structure of 2 $\mu{\rm m}$ is fabricated and shows quasi-single mode operation. The spacing of the lasing modes shows a clear dependence of the actual cavity lengths with fairly good agreement to theory taking account of the refractive index dispersion.