Influence of discharge parameters on the layer properties of reactive magnetron sputtered ZnO:Al films

Aluminum-doped ZnO layers have been prepared by reactive d.c. magnetron sputtering from Zn:Al (2 wt.%) targets onto unheated substrates (Si, glass, glassy carbon). In dependence on the O 2 partial pressure in the argon sputtering gas there exists a narrow process window around a p O2 (p Ar + p O2 )...

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Bibliographic Details
Published in:Thin solid films 1994-07, Vol.247 (1), p.15-23
Main Authors: Ellmer, K., Kudella, F., Mientus, R., Schieck, R., Fiechter, S.
Format: Article
Language:English
Subjects:
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Exact sciences and technology
Insulators
Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation
Optical properties of specific thin films
Physics
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Summary:Aluminum-doped ZnO layers have been prepared by reactive d.c. magnetron sputtering from Zn:Al (2 wt.%) targets onto unheated substrates (Si, glass, glassy carbon). In dependence on the O 2 partial pressure in the argon sputtering gas there exists a narrow process window around a p O2 (p Ar + p O2 ) ratio of 5–10% which yields transparent, low-resistance layers. The discharge voltage dependence on the oxygen partial pressure is a sensitive indicator for the oxidation state of the target surface and can be used for the regulation of the deposition process. Lower O 2 partial pressures yield metallic-like, opaque, but highly resistant layers. Higher oxygen partial pressures lead to transparent but highly resistant ZnO layers. Layers of lowest resistivity (5 × 10 −4 Ω cm) and highest optical transmission (90%) have a stoichiometric ratio Zn:O of 1.0 and exhibit the largest grains (≈40 nm) as has been measured by Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). By comparing the metallurgical Al content (using RBS) in the films with the carrier concentration (Hall and conductivity measurements) we obtain an overall electrical activation of aluminiu in the best case of about 60%. We found an exponential dependence of the specific resistance on the ZnO crystallite size which explains the strong dependence of the sheet resistance on the oxygen partial pressure.
ISSN:0040-6090
1879-2731
DOI:10.1016/0040-6090(94)90470-7