Indium-doped cadmium oxide films on MgO and Si substrates with ultra-wide ENZ regions and high Berreman performances

As a traditional epsilon near zero (ENZ) material, doped cadmium oxide (CdO) shows a high development potential in the field of optical phase modulation, optical nonlinearity enhancement, surface plasmon mode excitation, and other applications due to its wide-tunable ENZ wavelength (λ ENZ ) and low optical loss. In this work, we fabricated indium-doped cadmium oxide (In:CdO) thin films with different ENZ performances and conductivity behaviors deposited on single-crystal MgO and double-polished Si substrates using the radio-frequency (RF) magnetron sputtering method. Ultra-wide ENZ regions (1356nm-3677 nm) in the In:CdO films were achieved primarily by varying the oxygen partial pressure from 0% to 100%. Furthermore, high electron mobility (157cm 2 /V-s) was attained by modulating the substrate temperature. The films exhibiting high electron mobility and low imaginary part of permittivity at λ ENZ ( ε ENZ ′ ′ ) were utilized to design Berreman-type absorbers, enhancing absorption by stimulating the Berreman mode near their respective λ ENZ . A maximum absorption of 99.81%, a narrow, nearly perfect absorption (>98%) bandwidth of 38 nm, and a Q-factor of 8 were observed with incident p-polarized light from the substrate side, while film with higher electron mobility and a lower ε ENZ ′ ′ showed a narrower, nearly perfect absorption bandwidth and a higher Q-factor.