Optical microprism cavities based on dislocation-free GaN

• Published in: Applied physics letters 2020-12, Vol.117 (23)
• Main Authors: Hjort, Filip, Khalilian, Maryam, Bengtsson, Jörgen, Bengths, Marcus, Gustavsson, Johan, Gustafsson, Anders, Samuelson, Lars, Haglund, Åsa
• Format: Article
• Language: English
• Subjects: Applied physics; Atom and Molecular Physics and Optics; Atom- och molekylfysik och optik; Bragg reflectors; Condensed Matter Physics; Den kondenserade materiens fysik; Dislocation density; Electron beams; Finite element method; Fysik; Gallium nitrides; Holes; Nanowires; Natural Sciences; Naturvetenskap; Physical Sciences; Prisms; Q factors; Threading dislocations; Threshold currents
• ISSN: 0003-6951; 1077-3118; 1077-3118
• DOI: 10.1063/5.0032967

Three-dimensional growth of nanostructures can be used to reduce the threading dislocation density that degrades III-nitride laser performance. Here, nanowire-based hexagonal GaN microprisms with flat top and bottom c-facets are embedded between two dielectric distributed Bragg reflectors to create dislocation-free vertical optical cavities. The cavities are electron beam pumped, and the quality (Q) factor is deduced from the cavity-filtered yellow luminescence. The Q factor is ∼500 for a 1000 nm wide prism cavity and only ∼60 for a 600 nm wide cavity, showing the strong decrease in Q factor when diffraction losses become dominant. Measured Q factors are in good agreement with those obtained from quasi-3D finite element frequency-domain method and 3D beam propagation method simulations. Simulations further predict that a prism cavity with a 1000 nm width will have a Q factor of around 2000 in the blue spectral regime, which would be the target regime for real devices. These results demonstrate the potential of GaN prisms as a scalable platform for realizing small footprint lasers with low threshold currents.