(a) Geometrical layout of the proposed flatband resonant metasurface. Periodic GaAs (made from [110] cut GaAs) metasurface with a period of P in x-direction and S × P in y-direction and thickness of 300 nm. S represents a non-zero scaling factor, which gives a different pitch in x- and y- directions. The substrate SiO₂ is not shown for simplicity. (b) & (c) shows the geometry engineering introduced to respectively generate high-Q and flatband features.