Fig. 1. (Color online) Schematic diagram of optimal growth path of GaN single crystal.

Fig. 2. (Color online) CL image of (a) traditional GaN substrate. (b) GaN substrate improved by HVPE technology.

Fig. 3. (Color online) (a) TEM image of InGaN/GaN SLs. (b) PL characteristics of sample A and sample B, where sample A is a conventional InGaN lower waveguide layer device, sample B is an InGaN/GaN SLs lower waveguide layer device.

Fig. 4. (Color online) AFM images of ECR-deposited (AR)-Al₂O₃-pre optimization (a), (HR)-Al₂O₃/Ta₂O₅-pre optimization (b), (AR)-Al₂O₃-post optimization (c), and (HR)-Al₂O₃/Ta₂O₅-post optimization (d) on GaN cleaved facets.

Fig. 5. (Color online) (a) The Power-Current-Voltage (PIV) as well as WPE characteristics of the LD. (b) Spectra of the LD, the illustration is a microscopy image of the GaN laser during light emission.