We can force the epi plug to maintain high doping and taller height, but the strain relaxation must come from dislocations. These changes in lattice strain could be interfacial, due to interfacial dislocations, or they could also originate from bulk. Such dislocations lower the overall crystallinity of the epitaxial plug, giving some regions of low crystallinity inside a highly monocrystalline epitaxial plug. Whereas a lower doping will result in smaller lattice mismatch. This small lattice mismatch will also result in a lower lattice strain. Such low lattice strains allow the epitaxial plug to grow taller without losing any of the lattice strain. The critical thickness, the thickness for which the lattice remains strained, is given by :