

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 inplane 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]. 

The nonzero strain terms for uniaxial external strain in [110], [100] and [001] directions are:
where S_{11}, S_{12} and S_{44} are compliance constants. The final strain is the sum of (43) and (44).
