Infrared Plasmonics via ZnO

Abstract

Conventional plasmonic devices involve metals, but metal-based plasmonic resonances are mainly limited to λres < 1 μm, and thus metals interact effectively only with light in the UV and visible ranges. We show that highly doped ZnO can exhibit λres ≥ 1 μm, thus moving plasmonics into the IR range. We illustrate this capability with a set of thin (d = 25–147 nm) Al-doped ZnO (AZO) layers grown by RF sputtering on quartz glass. These samples employ a unique, 20-nm-thick, ZnON buffer layer, which minimizes the strong thickness dependence of mobility (μ) on thickness (d). A practical waveguide structure, using these measurements, is simulated with COMSOL Multiphysics software over a mid-IR wavelength range of 4–10 μm, with a detailed examination of propagation loss and plasmon confinement dimension. In many cases, Lplas < λlight, thus showing that IR light can be manipulated in semiconductor materials at dimensions below the diffraction limit.