We disclose herein an infra-red (IR) device comprising a substrate comprising an etched cavity portion and a substrate portion; a dielectric layer disposed on the substrate. The dielectric layer comprises a dielectric membrane which is adjacent, or directly above, or below the etched cavity portion of the substrate. The device further comprises a reflective layer on or in or above or below the dielectric membrane to enhance emission or absorption of infrared light at one or more wavelengths.