Low-threshold GaN surface emitting lasers: A comparative study of circular grating and photonic crystal designs

Abstract We demonstrate room-temperature pulsed lasing of two types of GaN-based surface emitting lasers (SEL) fabricated without epitaxial regrowth. We present a direct comparison between a circular grating (CGSEL) and a photonic crystal (PCSEL) design. The devices are realized by etching the photonic structures directly into the p-GaN cladding, and utilizing a patterned indium tin oxide (ITO) top contact. Both designs exhibit lasing near 438 nm under pulsed current injection. The CGSEL, incorporating a central defect, achieves a low threshold current density (<1 kA/cm 2 ) and a small divergence angle (≈0.15°) by coupling to a bandgap defect mode. In contrast, the PCSEL shows a higher threshold current density and lases on a 1D band-edge mode, resulting in a cross-shaped far-field pattern. These results confirm the regrowth-free method as a viable route for manufacturable GaN SELs. Crucially, the comparative study identifies the CGSEL defect-mode design as a more robust path toward high-performance lasing in low-confinement epitaxial structures.