Chemical Boundary Layers in MOCVD: The Return of the Stagnant Layer
Boundary layers always have played an important rôle in theories and studies about CVD. From these studies it has become clear that velocity and temperature boundary layers indeed are present for the initial part of the susceptor (cm’s to dm’s) where the flow and temperature fields still have to develop. The consequence is that if one has a short susceptor or a high throughput velocity one nearly always has to cope with a less controlled situation which does not lend itself easily for quantitative predictions of growth rates, or to put it even more drastically, is not really suited for measuring chemical rate constants. This situation slowly changes in favour of MOCVD performed in well established flow and T-profiles, realized in longer cells where physical boundary layers no longer are present.