Wideband Tunable Omnidirectional Infrared Absorbers Based on Doped Silicon Nanowire Arrays

Abstract

The present study considers the directional and spectral radiative properties of vertically aligned, heavily doped silicon nanowires for applications as broadband infrared diffuse absorbers. The nanowire array is modeled as a uniaxial medium whose anisotropic dielectric function is based on an effective medium theory. The approximation model is verified by the finitedifference timedomain method. It is found that the radiative properties of this type of nanostructured material could be tailored by controlling the doping concentration, volume filling ratio, and length of the nanowires. Increasing the wire length yields a broadening of the absorption plateau, while increasing the doping concentration results in a shift of the plateau to shorter wavelengths. Moreover, two kinds of omnidirectional absorbers/emitters could be realized based on the dopedsilicon nanowire arrays. The first one is a wavelengthtunable wideband absorber, which may be important for applications in thermal imaging and thermophotovoltaic devices. The second acts as a quasiblackbody in the wavelength region from 3 to 17 خ¼m and, therefore, is promising for use as an absorber in bolometers that measure infrared radiation and as an emitter in space cooling devices that dissipate heat into free space via thermal radiation.