Notions of Hydrodynamics

The flow of precursor gases to the surface of the substrate plays an important role in the kinetics of growth and also on the uniformity and quality of the crystalline films. 

The gas flow is laminar when Re 5,400 the forces of friction stabilize the flow. 

In a cold wall reactor, the convection regime is mixed. On the one hand, the temperature gradient between the substrate and the walls of the reactor tends to establish a system of natural convection (laminar flow). On the other hand, the flow of gas induces a forced convection (turbulent flow). A laminar flow is necessary to ensure a good uniformity of the epitaxial film thickness. 

---