Cooling Epitaxy

Under these conditions, anatase transforms into rutile and V O melts. On cooling, epitaxial relationships are formed between (010) V O and (110) of rutile. Since the electronic properties of rutile are very close to anatase, the same explanations apply. 

Figure 11. Calculated epitaxial layer thickness as a function of time for equilibrium, step-cooling, and supercooling temperature programs. (Reproduced with permission from reference 94. Copyright 1984 American Institute of...

Figure 13. Thickness of InGaAsP epitaxial layers versus growth time for growth by the step-cooling technique with 10 °C supersaturation. (Reproduced with permission from reference 100. Copyright 1980 American Institute of...

A silicone rubber adhesive layer is used in US-A-4081819 to bond an HgCdTe substrate, which includes an epitaxial layer, to a second substrate. The silicone rubber adhesive reduces the risk that the substrate cracks when cooled to cryogenic temperatures. 

To obtain this composition, a metallic solvent is contacted with a silicon source at this temperature Ta during few hours. This leads to the saturation of the solvent in Si, at Xa concentration. Then, the silicon source is removed. If this liquid is brought into contact with a silicon substrate at this temperature, the equilibrium is not changed. However, when the solution is cooled down to Tb, the system presents two phases silicon solid phase appears and the new concentration of the liquid phase in Si becomes Xc. If the cooling process is slow (few Kelvin per minute or less), parasite germination rate within the solvent is close to zero and epitaxial deposition of silicon occurs only on the substrate. 

The thickness of the epitaxial layer depends on the temperature, solvent, cooling rate and amount of solvent and silicon, i.e. the weight of the melt compared to the surface of the substrate. 

The experiments were done under the following conditions 7 g of Sn (purity 5N), 2h of growth, 0.5°C min-1 cooling rate. Since the amount of silicon incorporated in the melt increases with the temperature, it is possible to grow thick epitaxial layers. However, for low-temperatures (700-800°C), incorporation of silicon is low and limits the kinetics of growth. At this temperature range, thermodynamic properties of metallic alloys can increase the kinetics (see Sect. 9.6). 

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