Mid-infrared angle-resolved spectral characteristics of photonic crystal slabs for application in surface-emitting quantum cascade lasers

We study the angle-dependent reflection spectra of two-dimensional photonic crystal (PC) slabs, which we use for developing mid-infrared surface-emitting lasers. The PC design produces a perfect resonance between material gain frequencies and the F-point band edge in the first Brillouin zone. Hence, we expect laser emission to occur in a direction normal to the slab surface. We fabricate PC slabs, which consist of a square lattice of nanopillars with different lateral cross-sections, i.e., circles, triangles, and pentagons, and discuss their impact on the mode characteristics. We consider that our angle-resolved spectroscopic technique will be useful for characterizing mid-infrared PC slabs to be used in vertical surface-emitting quantum cascade lasers.