GaN Substrate Surface Control for Higher Laser Diode Yield

The patent applies preliminary action by introducing a buffer layer structure before the active GaN crystal growth. The buffer layer is grown first to prepare the substrate surface, then the GaN crystal is grown on top of it. This preliminary buffer layer formation prevents direct contact between the substrate and the growing crystal, reducing the generation of local strains and pits during the HVPE process while maintaining ease of manufacture.

The patent applies parameter changes by optimizing the HVPE growth conditions including temperature gradients, pressure, and gas flow rates during crystal growth. By carefully controlling these parameters, the method achieves reduced dislocation density and fewer local strains on the main surface while maintaining a relatively simple single-step HVPE process, thus improving substrate quality without significantly increasing production complexity.

The patent applies self-service by designing a buffer layer structure that automatically compensates for surface irregularities during the GaN crystal growth process. The buffer layer self-adjusts to create a flat main surface with minimal local strains without requiring additional post-growth polishing or correction steps. This self-correcting mechanism improves laser diode yield while avoiding the need for extremely high manufacturing precision in subsequent processing steps.