L12-Epitaxy

L12-Epitaxy - Epitaxy Epitaxial Growth Epitaxy means the...

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Epitaxy
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Epitaxial Growth ± Epitaxy means the growth of a single crystal film on top of a crystalline substrate. ± For most thin film applications (hard and soft coatings, optical coatings, protective coatings) it is of little importance. ± However, for semiconductor thin film technology it is crucial.
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Types of Epitaxy ± Homoepitaxy ² The film and the substrate are the same material. ² Often used in Si on Si growth. ² Epitaxially grown layers are purer than the substrate and can be doped independently of it. ± Heteroepitaxy ² Film and substrate are different materials. ² Eg: AlAs on GaAs growth ² Allows for optoelectronic structures and band gap engineered devices.
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Heteroepitaxy ± Trying to grow a layer of a different material on top of a substrate leads to unmatched lattice parameters. ± This will cause strained or relaxed growth and can lead to interfacial defects. ± Such deviations from normal would lead to changes in the electronic, optic, thermal and mechanical properties of the films.
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Lattice Strains ± For many applications nearly matched lattices are desired to minimize defects and increase electron mobility. ± As the mismatch gets larger, the film material may strain to accommodate the lattice structure of the substrate. This is the case during the early stages of film formation (pseudomorphic growth) and with materials of the same lattice structure. The Si-Ge system is an example. ± If strain accommodation is not possible then dislocation defects at the interface may form leading to relaxed epitaxy and the film returns to its original lattice structure above the interface. ± Lattice misfit is defined as: Matched Strained Relaxed Substrate Substrate Substrate Film Film Film ±² ± ² >@ ± ² fa sa 0 0 0 f ³ where a 0 ( s/f ) are the lattice constants of the substrate and the film.
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Metal-Semiconductor Heteroepitaxy ± Metal-semiconductor structures are used for contact applications. ± While not essential, epitaxial growth allows increased electron mobility through a junction. ± Examples: ² CoSi 2 or NiSi 2 on Si. Since the lattice mismatch is small (all around 5.4 ǖ ) and the crystal structures are similar, interfaces are remarkably defect free. ² Fe on GaAs is similarly possible since the lattice size of Fe is about half of GaAs.
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L12-Epitaxy - Epitaxy Epitaxial Growth Epitaxy means the...

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