Epitaxial crystallinity

The lattice mismatch between silicon and mercury cadmium telluride makes it difficult to grow an epitaxial crystalline layer of mercury cadmium telluride on silicon. In EP-A-0343738 an imager is formed by growing mercury cadmium telluride on a sapphire substrate at openings formed in a silicon layer which has been grown on the sapphire substrate (silicon-on-sapphire, SOS) at an earlier stage. 

When the melt or the solutions are stirred epitaxial crystallinity is usually observed. One crystalline growth occurs right on top of another. This arrangement is often caUed shish-kebab... 

C and (e) its final epitaxial crystalline structure after cooling to room temperatnre (e). Chang et al. [174]. Reproduced with permission of American Chemical Society. 

The contribution of the surface/interface can be neglected in most cases. However, it plays an important role when the bulk volume of the crystalline phase is small. This is the case in the initial phase of crystal formation or when a thin (epitaxial) crystalline layer is formed. In the latter case besides the energy of free or unstrained interfaces the elastic strain imposed by coherent intergrowth with the substrate of different lattice constant also provides a contribution to the total energy balance that can not be neglected. 

The oriented overgrowth of a crystalline phase on the surface of a substrate that is also crystalline is called epitaxial growth [104]. Usually it is required that the lattices of the two crystalline phases match, and it can be a rather complicated process [105]. Some new applications enlist amorphous substrates or grow new phases on a surface with a rather poor lattice match. 

The growth of a well ordered fullerene monolayer, by means of molecular beam epitaxy, has been used for the controlled nucleation of single crystalline thin films. The quality and stability of molecular thin films has been shown... 

Silicon Epitaxy. A critical step ia IC fabricatioa is the epitaxial depositioa of sdicoa oa an iategrated circuit. Epitaxy is defined as a process whereby a thin crystalline film is grown on a crystalline substrate. Silicon epitaxy is used ia bipolar ICs to create a high resistivity layer oa a low resistivity substrate. Most epitaxial depositioas are doae either by chemical vapor depositioa (CVD) or by molecular beam epitaxy (MBE) (see Thin films). CVD is the mainstream process. 

The epitaxy reactor is a specialized variant of the tubular reactor in which gas-phase precursors are produced and transported to a heated surface where thin crystalline films and gaseous by-products are produced by further reaction on the surface. Similar to this chemical vapor deposition (CVE)) are physical vapor depositions (PVE)) and molecular beam generated deposits. Reactor details are critical to assuring uniform, impurity-free deposits and numerous designs have evolved (Fig. 22) (89). 

X-ray Diffraction (XRD) is a powerful technique used to uniquely identify the crystalline phases present in materials and to measure the structural properties (strain state, grain size, epitaxy, phase composition, preferred orientation, and defect structure) of these phases. XRD is also used to determine the thickness of thin films and multilayers, and atomic arrangements in amorphous materials (including polymers) and at inter ces. 

As we have seen, the orientation of crystallites in a thin film can vary from epitaxial (or single crystalline), to complete fiber texture, to preferred orientation (incomplete fiber texture), to randomly distributed (or powder). The degree of orientation not only influences the thin-film properties but also has important consequences on the method of measurement and on the difficulty of identifying the phases present in films having multiple phases. 

Another recently discovered form of epitaxy is graphoepitaxy (Geis et al. 1979). Here a non-crystalline substrate (often the heat-resistant polymer polyi-mide, with or without a very thin metallic coating) is scored with grooves or pyramidal depressions the crystalline film deposited on such a substrate can have a sharp texture induced by the geometrical patterns. More recently, this has been tried out as an inexpensive way (because there is no need for a monocrystalline substrate) of preparing oriented ZnS films for electroluminescent devices (Kanata et al. 1988). 

Thin polymer films may also be investigated by TEM and high resolution images are obtained for e.g. thin films of liquid crystalline polymers [64]. Usually thin microtome cuts from bulk samples are investigated, but also epitaxial growth of polyoxymethylene on NaCl [152], chain folding of polyethylene crystals [153], epitaxial crystallization of polypropylene on polystyrene [154] or monomolecular polystyrene particles [155] are observed. The resolution is, however, in most cases not comparable to STM. 

The nature of the deposit and the rate of nucleation at the very beginning of the deposition are affected, among other factors, by the nature of the substrate. A specific case is that of epitaxy where the structure of the substrate essentially controls the structure of the deposit.Plb lP ] Epitaxy can be defined as the growth of a crystalline film on a crystalline substrate, with the substrate acting as a seed crystal. When both substrate and deposit are of the same material (for instance silicon on silicon) or when their crystalline structures (lattice parameters) are identical or close, the phenomena is known as homoepitaxy. When the lattice parameters are different, it is heteroepitaxy. Epitaxial growth cannot occur if these stmctural differences are too great. 

This reaction is irreversible. Epitaxial silicon is deposited. Polycrystalline silicon is obtained in the range of 610-630°C, which is close to the crystalline-amorphous transition temperature. 

Epitaxy is a term that denotes the growth of a thin crystalline film on a crystalline substrate. When the epitaxial film is of the same material as the substrate (for instance silicon on silicon), the process is known as homoepitaxy. When film and substrate are of different... 

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