Abstract
Zinc oxide films doped with 0 at. %–5 at. % aluminum are fabricated by flow-limited field-injection electrostatic spraying using a sol–gel processed precursor. X-ray diffraction and Rietveld analyses indicate that the films are highly (002)-oriented with large crystallites and that the lattice constants of the doped-ZnO tend to decrease with Al doping below the values of undoped-ZnO. Optical properties were measured by ellipsometry and analyzed using the Drude model of permittivity. The electron scattering rate is calculated to be minimal at 3 at. % Al, which may indicate a reduction in the ionized impurities due to the lattice strain and the absence of Al clusters, which is enabled by the sol–gel precursor. Insights are offered regarding the effects of Al doping on film density, electron concentration, and background permittivity, which may prove important in tuning the film properties for plasmonic applications.
Highlights
Aluminum-doped zinc oxide (AZO) is a transparent conducting oxide (TCO) of interest in plasmonic applications due to its higher mobility and, lower optical loss compared to other TCOs such as indium-doped tin oxide or gallium-doped ZnO.[1]
Flow-limited field-injection electrostatic spraying (FFESS) deposition of AZO films with 0 at. %–5 at. % Al doping was subsequently performed on c-plane sapphire substrates at 350 ○C in ambience
It is well known that crystallographic orientations of oxide films are affected by various factors, e.g., precursor chemistry and the processing conditions
Summary
Aluminum-doped zinc oxide (AZO) is a transparent conducting oxide (TCO) of interest in plasmonic applications due to its higher mobility and, lower optical loss compared to other TCOs such as indium-doped tin oxide or gallium-doped ZnO.[1]. AZO offers tunable optical response that can be controlled by the amount of doping.[2,3,4,5] Previous studies, both theoretical and experimental, have indicated that a minimal resistivity in AZO is achieved by optimizing Al doping to maximize the free carrier concentration without degrading the crystallinity and reducing the mobility.[6,7,8] The electron scattering rate for DC conduction in AZO was reported to be dominated by grain-boundary scattering, prompting the growth of large grains.[9,10] this effect is not as relevant at high frequencies, rendering ionized-impurity scattering more important for optical systems.[11,12] Systematic studies on the optical response of AZO under differing Al stoichiometries may further elucidate the scattering mechanisms at optical frequencies
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