Influence of Backside Surface and Subsurface Damage in Gallium Nitride Wafers on Facet Quality and Violet‐Emitting Laser Diode Performance

Backside wafer thinning is crucial for producing high‐performance GaN laser, as it enables precise cleavage and the formation of high‐quality facets. This study investigates the effects of thinning techniques—lapping with different abrasive sizes, grinding, and mechanical polishing—on surface and subsurface damage (SSD) in GaN wafers, and examines how backside properties influence cleaved facets and device performance. Compared to lapping, grinding produces lower surface roughness, reduces SSD by up to a factor of five to 0.7 µm, and increases the wafer's bow radius by up to a factor of two to 0.65 m. Subsequent mechanical polishing yields a smoother surface, eliminates SSD, and further increases the bow radius to 2.2 m. The improved surface reduces the risk of unintentional wafer breakage from thinning‐induced damage, stress, and tensile strain in epitaxial layers. X‐ray diffraction confirms enhanced crystallinity with polished surfaces and finer abrasives. A clear correlation emerges between SSD, terrace formation on laser facets, and device performance. Lapping produces the roughest facets and the highest, most scattered threshold currents, while grinding and polishing yield smoother facets and reduce threshold current by nearly 40%. These findings highlight the critical role of backside surface quality in fabricating reliable, high‐performance GaN lasers.