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Theory
Strain effects
Strain effects in a heterostructure can be divided on internal and external. The internal strain is a result of lattice constant
mismatch. The grown on substrate layers copy the in-plane substrate lattice constant if the thickness of layers is below
critical one. In that case, the heterostructure layer has a biaxial tensile strain if the layer lattice constant is smaller than substrate one. In other case, when the layer lattice constant is larger than substrate one, the heterostructure layer has a
compressive strain. For the lattice matched strain the strain tensor has the following nonzero components:
where a0 and a are the lattice constant of the substrate and the layer material, C11 and C12 are the elastic stiffness constant.
A layer material with a lattice constant a to be grown on a substrate with a lattice constant a 0:
(a) unstrained; (b) strained [7]. |
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The nonzero strain terms for uniaxial external strain in [110], [100] and [001] directions are:
where S11, S12 and S44 are compliance constants. The final strain is the sum of (43) and (44).
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