Bubble-free laser slicing strategy for 2-inch gallium nitride wafers

This study proposes a low kerf-loss laser-slicing strategy for GaN wafers using a 10-picosecond laser to address the bottleneck of severe damage caused by gas bubbles in bulk GaN, which arise from thermal decomposition under laser irradiation. Based on the crystallographic anisotropy of wurtzite GaN and the multi-pulse incubation effect, the strategy constructs a directional gas-exhaust network to release N 2 before cavity-forming pressures are reached. Modified lines are scanned along the m-axis and densely arranged along the a-axis, forming interconnected crack‑bridged channels that suppress bubble formation. A dual‑threshold behavior (modification threshold vs. damage threshold) is identified, and the optimized parameters ( E L = 8.25 μJ/μm, d = 15 μm) yield bubble‑free internal modification of 2‑inch GaN wafers within 26 min, followed by ultrasonic separation in 5 min. Multi‑scale characterization (SEM, XRD, Raman, and HRTEM with EDS depth profiling) reveals a pronounced structural asymmetry: the upper surface exhibits a porous, amorphized layer (5–20 nm) with nitrogen depletion, while the lower surface preserves near‑intrinsic crystallinity, attributed to polarity‑dependent thermal decomposition. This work provides a scalable route for low‑kerf‑loss (∼56 ± 5 μm) GaN wafer slicing, with potential extension to other wide‑bandgap materials that generate gaseous decomposition products during laser processing.