**2.3. Factors governing the epitaxy growth**

The key factors governing epitaxy growths are structural compatibility, chemical compatibility, and growth temperatures.

**- Structural compatibility:** The structures of a film and a substrate should have good lattice matching in terms of crystal structures (*a*0, sub) and lattice constants (*a*0, film), that is, small lattice misfit.

Lattice misfit *f*:

$$f = \frac{a\_{0,sub} - a\_{0,film}}{a\_{0,film}} \approx \frac{a\_{0,sub} - a\_{0,film}}{a\_{0,sub}} \sqrt{2}.\tag{1}$$

**- Chemical compatibility:** This includes chemical bonding and chemical diffusion.

**- Growth temperatures:** Good epitaxy growth is obtained at above or around the well-defined elevated substrate temperature (*Te*). *Te* depends on the deposition rate, particle energy, and surface contamination. Generally, a higher temperature is recommended to reduce surface contamination by desorption (or enhance surface mobility) of atoms to reach the favorable sites and also enhance the diffusivity in deposition for favoring re-crystallization and defect annihilation.
