Development of ZnO films for near-IR plasmonics

Ga-doped ZnO grown at 200 °C by pulsed-laser deposition in Ar ambient and annealed face-down on Zn foil at 500 °C in forming gas can attain near-record electrical characteristics for ZnO: resistivity ρ = 1.23 × 10-4 Ω-cm, mobility μHall = 34.1 cm2/V-s, and free-electron concentration n = 1.4 x 1021 cm-3, leading to a plasmonic resonance wavelength λres = 1.05 μm. A value of λres near 1 μm is important because metal-based plasmonics are lossy in the IR region. Longer resonant wavelengths in ZnO, e.g., the telecommunication wavelengths λres = 1.3 and 1.55 μm, are then simply produced by furnace anneals in air. A relatively unexploited characterization tool for such materials is spectroscopic ellipsometry (SE). By harnessing the full potential of SE we demonstrate full-color maps of thickness d, concentration nSE, and mobility μSE.