UV-C Photonic-Crystal Surface-Emitting Lasers

Doctoral thesis, 2026

Semiconductor lasers are compact, coherent light sources that have enabled or transformed a wide range of applications since their invention in the 1960s. They have rapidly matured at visible and infrared wavelengths; however, their progress at ultraviolet-C (UV-C, λ<280 nm) wavelengths has been considerably slower. To date, continuous-wave electrically driven UV-C edge-emitting lasers have been reported, but vertical-cavity surface-emitting lasers have only been demonstrated under optical pumping. Photonic-crystal surface-emitting lasers (PCSELs), on the other hand, are a new type of semiconductor laser and have recently attracted attention for their unique optical properties. They combine watt-level single-mode output powers and circularly symmetric beams with low divergence angles below 1°. PCSELs have demonstrated strong performance at visible and infrared wavelengths, but were not realized in the UV-C before this work.


In this thesis, we demonstrate the first UV-C PCSELs operating at room temperature under pulsed optical pumping. We investigate the influence of photonic crystal design parameters, including hole filling factor, lattice constant, etch depth, and lateral photonic crystal size, on lasing characteristics and address the challenges in achieving lasing under electrical injection. Our results indicate that the lasing threshold of PCSELs decreases with increasing device size. Therefore, a larger size is beneficial for low-threshold operation. However, for large sizes (>100 μm), current injection across the device area is challenging due to the poor electrical conductivity of Al-rich AlGaN, which may prevent lasing. To reduce the current spreading distance and improve current uniformity, we introduce a ring-shaped photonic crystal design, where a central circular region is etched to accommodate an additional n-contact. These findings help better understand III-nitride-based UV-C PCSELs and open a pathway toward future electrically driven devices.