GaN-Based Blue Laser Diodes With 2.2 W of Light Output Power Under Continuous-Wave Operation

Research on GaN-based blue and green laser diodes (LDs) has attracted great attention in the past years to meet the demand for laser display application. In this letter, we improve luminescence homogeneity and reduce internal loss of GaN-based blue LD structures grown on <inline-formula> <tex-math notation="LaTeX">$c$ </tex-math></inline-formula>-plane free-standing GaN substrates. The morphologies of homoepitaxial GaN layers are greatly affected by offcut orientation and an angle of GaN substrates. Perfect morphology with straight atomic steps and regular terrace width can be obtained for GaN layers grown on GaN substrates with an offcut angle of 0.42° toward <inline-formula> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula>-plane. On GaN substrates with an offcut angle of 0.4° toward <inline-formula> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula>-plane, homoepitaxial LD structures grown utilizing the same growth temperature for InGaN quantum wells and GaN quantum barriers have narrowest emission linewidth and very homogeneous luminescence. The internal loss is greatly reduced by optimizing Mg doping profile. As a result, we have achieved GaN-based blue laser diodes with 2.2 W of light output power under continuous-wave operation at room temperature.