Ultralow threshold surface emitting ultraviolet lasers with semiconductor nanowires

Abstract

Surface-emitting (SE) semiconductor lasers have changed our everyday life in various ways such as communication and sensing. Expanding the operation wavelength of SE semiconductor lasers to shorter ultraviolet (UV) wavelength range further broadens the applications to disinfection, medical diagnostics, phototherapy, and so on. Nonetheless, realizing SE lasers in the UV range has remained to be a challenge. Despite of the recent breakthrough in UV SE lasers with aluminum gallium nitride (AlGaN), the electrically injected AlGaN nanowire UV lasers are based on random optical cavities, whereas AlGaN UV vertical-cavity SE lasers (VCSELs) are all through optical pumping and are all with large lasing threshold power densities in the range of several hundred kW/cm2 to MW/cm2. Herein, we report ultralow threshold, SE lasing in the UV spectral range with GaN-based epitaxial nanowire photonic crystals. Lasing at 367 nm is measured, with a threshold of only around 7 kW/cm2 (~ 49 μJ/cm2), a factor of 100× reduction compared to the previously reported conventional AlGaN UV VCSELs at similar lasing wavelengths. This is also the first achievement of nanowire photonic crystal SE lasers in the UV range. Further given the excellent electrical doping that has already been established in III-nitride nanowires, this work offers a viable path for the development of the long-sought-after semiconductor UV SE lasers.

Architecture for Surface-Emitting Lasers with On-Demand Lasing Wavelength by Nanowire Optical Cavities

“…III-Nitrides have ultrawide bandgap energies ranging from NIR to UV, meaning a wide range of optical gain can be supported, which makes them especially appealing for SE lasers with a wide operational wavelength range. III-Nitride epi-NPC lasers have emerged in recent years. − For these lasers, the formation of epi-NPCs often requires SAE at high substrate temperatures on patterned substrates. Such a high substrate temperature can lead to poor selectivity and less controllability of nanowires and thus affect the NPC formation, e.g., refs − .…”

“…On the other hand, semiconductor nanowires have been a fascinating platform for lasers. Back two decades ago, lasing from single semiconductor nanowires has already been demonstrated. − Recent years have also witnessed the application of semiconductor nanowires into large scale SE lasers using photonic crystal band edge modes, which eliminate the need for problematic DBRs in conventional VCSELs for the optical cavity formation. − In addition, nanowires offer other advantages such as improved material quality and electrical doping, compared to planar counterparts. − …”