Enhanced light absorption in Tamm metasurface with a bound state in the continuum

We consider light absorption in a germanium grating placed on top of photonic-crystalline substrate. Such system supports an optical Tamm state decoupled from the continuous spectrum with its frequency within photonic band gap. have demonstrated that application makes possible to engineer extremely narrow absorber which provides 100% semiconductor critical coupling regime. The proposed design may be used at both normal and oblique incidence telecom wavelength.