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Epitaxial Aluminum‐Doped Zinc Oxide Thin Films on Sapphire: II, Defect Equilibria and Electrical Properties
Author(s) -
Srikant V,
Sergo Valter,
Clarke David R.
Publication year - 1995
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1995.tb08913.x
Subject(s) - sapphire , zinc , epitaxy , doping , materials science , aluminium , thin film , aluminum oxide , oxide , inorganic chemistry , chemical engineering , optoelectronics , metallurgy , chemistry , nanotechnology , layer (electronics) , optics , laser , physics , engineering
The electrical transport properties of epitaxial ZnO films grown on different orientations of sapphire substrates have been measured as a function of partial pressure of oxygen. After equilibration, the carrier concentration is found to change from a p ‐1/4 O2 to a p ‐3/8 O2 dependence with increasing oxygen partial pressure. The partial pressure dependence is shown to be consistent with zinc vacancies being the rate‐controlling diffusive species. In addition, the carrier concentration in ZnO films grown on A‐, C‐, and M‐plane sapphire are the same but that of R‐plane sapphire is systematically lower. Electron Hall mobility measurements as a function of carrier concentration for all the substrate orientations exhibit a transition from “single‐crystal” behavior at high carrier concentrations to “polycrystalline” behavior at low carrier concentrations. This behavior is attributed to the effective height of potential barriers formed at the low‐angle grain boundaries in the epitaxial ZnO films. The trap density at the grain boundaries is deduced to be 7 × 10 12 /cm 2 . The electron mobility, at constant carrier concentration, varies with the substrate orientation on which the ZnO films were grown. The difference is attributed to the difference in dislocation density in the films produced as a result of lattice mismatch with the different sapphire orientations.