N-Ge on Si for mid-infrared plasmonic sensors

Plasmonic materials have the free electron oscillations in a metal coupled to photons and allow near field amplification of radiation below the plasmon edge. Metals such as Au and Ag can be used for visible wavelengths but these materials are incompatible with silicon foundries due to fast diffusion and the deep level trap states formed. Heavily doped semiconductors well above the Mott metal-insulator transition criteria can be used as plasmonic materials for the mid-infrared wavelengths where many molecules have strong molecular absorption lines related to the bonds which allow identification. Here n-Ge epitaxially grown on Si substrates is used as a mid-infrared plasmonic material and plasmonic antennas are demonstrated to provide amplification of specific molecular absorption lines of chemical weapon simulants. Examples of mid-infrared plasmonic sensors will be presented with potential applications for healthcare, environmental and chemical, biological, radiological, nuclear and explosives (CBRNE) security sensing.