Impact of Air Hole Geometry on the Performance of InGaN/GaN Photonic Crystal Surface-Emitting Lasers

In this study, we demonstrate GaN-based photonic crystal surface-emitting lasers (PCSELs) employing two distinct air hole geometries: circular (CC) and right-isosceles-triangle (RIT). By systematically tuning the fill factor (FF) and lattice constant, the lasing wavelengths are maintained between 420–425 nm, enabling direct comparison of device performance. Optical simulations and experimental results confirm that the CC structure, characterized by high in-plane symmetry (C4vgroup), supports degenerate Bloch modes at the Γ point, resulting in strong lateral confinement, low vertical radiation loss, and high Q-factors. These features enable low-threshold lasing. In contrast, the RIT structure intentionally breaks the in-plane rotational symmetry, lifting mode degeneracy via geometric asymmetry. This mode splitting selectively enhances the vertical radiation coupling of the desired B-mode while suppressing competing modes, facilitating stable single-mode operation. Although the RIT design yields a higher threshold due to the increased vertical loss, it also demonstrates superior slope efficiency beyond the threshold. The declining threshold trend with increasing FF in both configurations matches the simulated predictions.