Wide-bandgap optical materials for high-harmonics generation at the nanoscale

High-order harmonics generation (HHG) is the only process that enables table-top-size sources of extreme-ultraviolet (XUV) light. The HHG process typically involves light interactions with gases or plasma-material phases that hinder wider adoption of such sources. This motivates the research in HHG from nanostructured solids. Here we investigate theoretically material platforms for HHG at the nanoscale using first-principle supercomputer simulations. We reveal that wide bandgap semiconductors, aluminium nitride AlN and silicon nitride SiN, are highly promising for XUV light generation when compared to one of the most common nonlinear nanophotonic material -- silicon. In our calculations we assume excitation with 100 fs pulse duration, 10^13 W/cm^2 peak power and 800 nm central wavelength. We demonstrate that in AlN material the interplay between the crystal symmetry and the incident light direction and polarization can enable the generation of both even and odd harmonics. Our results should advance the developments of high-harmonics generation of XUV light from nanostructured solids.