Berreman type perfect absorber based on epsilon near zero material gallium doped zinc oxide

Abstract

Optical performances of epsilon near zero (ENZ) material gallium doped zinc oxide (GZO) can be effectively tuned by modulating substrate types, substrate heating temperatures, as well as post-annealing procedures. Four GZO film samples with imaginary part of permittivity at their ENZ wavelengths of εENZ ′′  = 0.26, 0.32, 0.50, 0.68 were deposited with radio frequency magnetron sputtering technology, all samples could reach perfect absorption at a certain incident angle and wavelength. A smaller εENZ ′′ of GZO film provides narrower bandwidth of near perfect absorption peak (higher Q-factor), while a larger εENZ ′′ tends to have a broader bandwidth. Furthermore, the incident angle allowed to achieve perfect absorption is also influenced by εENZ ′′ of GZO films. To realize near perfect absorption (reflectivity below 5%), larger εENZ ′′ provides a wider near perfect absorption window (Δθ); smaller εENZ ′′ tends to have an easier condition to achieve perfect absorption.