Research Progress on GaN-Based Photonic Crystal Surface-Emitting Lasers

Conventional edge-emitting lasers and vertical-cavity surface-emitting lasers struggle to achieve high output power, high beam quality, and planar integration simultaneously. Photonic crystal surface-emitting lasers (PCSELs) exploit the band-edge resonance principle of two-dimensional photonic crystals, enabling large area single mode operation, vertical surface emission, and near diffraction limited beam output. They represent a key device to overcome the aforementioned bottlenecks. Gallium nitride (GaN)-based materials provide an ideal platform for short wavelength lasers in the blue and green spectral regions. Blue wavelengths offer favorable physical properties including a low-threshold current, high optical intensity, and high brightness. Moreover, blue lasers show indispensable application value in underwater communication and precision processing of highly reflective metals. GaN-based PCSELs combine the structural benefits of PCSELs with the material benefits of GaN, making them a research hotspot for high-performance visible coherent light sources. This review systematically describes the operating principle of PCSELs and the theoretical model of GaN-based PCSELs, outlines key device fabrication processes, and highlights representative research achievements from 2008 to the present, covering the evolution from optically pumped to watt-class electrically injected devices and from blue to green wavelengths. The review also analyzes the performance improvements brought by innovative designs such as honeycomb lattices, dual lattice structures, quasi crystal patterns, and regrowth free processes. It summarizes the main technical challenges, including lattice mismatch, complex fabrication, heat dissipation, and reliability issues, and finally discusses possible future directions for the field. This review aims to provide a reference for the design and optimization of high-brightness blue coherent sources.