Ultrafast vector laser processing of GaN in both linear and nonlinear regimes

Area of Science:

• Materials Science
• Laser Physics
• Semiconductor Processing

Background:

• Femtosecond laser ablation enables high-precision processing of wide-bandgap semiconductors like gallium nitride (GaN).
• Conventional Gaussian beams cause thermal issues due to concentrated energy, limiting processing efficiency.
• Laguerre-Gaussian (LG) beams offer potential advantages with their annular energy distribution, but their thermal dynamics are unquantified.

Purpose of the Study:

• To develop a unified multiphysics model for analyzing GaN thermal responses under Gaussian and LG beam irradiation.
• To comparatively investigate the nonlinear, spatiotemporal thermal dynamics during ultrafast laser processing.
• To quantify the benefits of LG beams over Gaussian beams for GaN ablation.

Main Methods:

• Coupling vectorial diffraction theory with a nonlinear two-temperature model.
• Dynamically incorporating multiphoton absorption, impact ionization, and Drude-based reflectivity corrections.
• Simulating femtosecond laser pulse interactions with GaN using both Gaussian and LG beams.

Main Results:

• LG beams redistribute optical energy, significantly reducing the maximum radial lattice-temperature gradient compared to Gaussian beams.
• The hollow structure of LG beams leads to expanded effective molten coverage.
• Reduced thermal gradients and expanded molten zones suggest improved theoretical geometric scanning efficiency.

Conclusions:

• LG beams offer a superior spatial energy distribution for femtosecond laser ablation of GaN.
• The developed multiphysics model provides a quantitative understanding of thermal dynamics in laser-semiconductor interactions.
• LG beams show promise for enhancing the efficiency and precision of GaN processing applications.