Mid-wave to near-IR optoelectronic properties and epsilon-near-zero behavior in indium-doped cadmium oxide

Engineering the Dispersion of Surface Plasmon Polariton/Epsilon‐Near‐Zero Modes through Modal Separation and Optical Confinement

“…The carrier tunability of the plasma frequency in doped semiconductors and transparent conducting oxides (TCOs) offers considerable control over the optical properties of these materials both during film growth [ 18–22 ] and through active modulation. [ 23,24 ] However, while this offers a mechanism for achieving some control over the SPP dispersion within the IR, the spectral dispersion and the group velocity cannot be controlled independently solely through changes to the carrier density.…”

“…In this work, we leverage the exciting properties of n‐doped CdO in order to explore strong coupling in multilayer CdO films, achieving unprecedented control over the polaritonic dispersion. CdO is a TCO that has garnered significant attention recently as a low loss (electron mobilities exceeding ), [ 21,22,40,41 ] broadly tunable () [ 20 ] infrared plasmonic material that can be grown using molecular beam epitaxy or high power impulse magnetron sputtering (HiPIMS). [ 42,43 ] In addition to supporting low‐loss SPP resonances, n‐doped CdO has been shown to exhibit sharp, highly absorptive ENZ‐polariton and Berreman modes in deeply subwavelength films (<120 nm).…”

“…Establishing methods to control the polaritonic dispersion of these lightmatter excitations has been of great interest as the nonzero group velocity (v g ¼ ∂ω ∂k ) and high confinement make SPPs useful for a broad range of nanophotonic applications including thermal emissivity control [2][3][4][5][6][7][8] and sensing, [9] surface-enhanced Raman scattering (SERS), [10][11][12][13][14][15] as well as in-plane nano-scale waveguiding. [16,17] The carrier tunability of the plasma frequency in doped semiconductors and transparent conducting oxides (TCOs) offers considerable control over the optical properties of these materials both during film growth [18][19][20][21][22] and through active modulation. [23,24] However, while this offers a mechanism for achieving some control over the SPP dispersion within the IR, the spectral dispersion…”

“…[42,43] In addition to supporting low-loss SPP resonances, n-doped CdO has been shown to exhibit sharp, highly absorptive ENZ-polariton and Berreman modes in deeply subwavelength films (<120 nm). [20,40] These novel optical excitations are associated with an extreme confinement of the electromagnetic fields within the film volume and a modal dispersion that becomes nominally flat. [44,45] Therefore, in the absence of losses, these modes are non-propagative, as their phase and group velocities diverge toward infinity and zero, respectively.…”

Tunable, Homoepitaxial Hyperbolic Metamaterials Enabled by High Mobility CdO

“…This was first demonstrated using doped and undoped InAs, however, its hyperbolic modes were limited to the long-wavelength IR (LWIR), and Poisson calculations revealed high carrier diffusion between layers when the carrier density difference was low or the individual layer thickness was reduced to ≈ 50 nm, limiting the design space and optical confinement. [17] Cadmium oxide (CdO) is an attractive candidate to overcome these challenges and create single-material HMMs with low optical loss and broader spectral tunability (2-9 µm wavelengths [32,33] ). Sophisticated fabrication techniques like molecular beam epitaxy (MBE) [34] and high-power impulse magnetron sputtering (HiPIMS) [32,35,36] produce CdO thin films with consistently high crystal quality that enables high mobilities for a TCO (up to 500 cm 2 V −1 s −1 ), and thus relatively low optical losses.…”