Epitaxy epitaxial phase diagram

The simplified analysis outlined above pertains directly to the epitaxial phase diagram of Dy in fig. 7. It suggests that the effect of clamping is not in fact negligible. 

Fig. 14. Phase diagrams of HgCdTe used to defiae the Hquid-phase epitaxial growth process where composition is ia mole fractioa, X, and the numbers represent temperatures ia °C (a) Te-rich corner where the dotted Haes A—F correspoad to values of of 0.1, 0.2, 0.3, 0.5, 0.8, and 0.9, respectively, and (b) Hg-rich corner where A—F correspond to values of X of 0.9, 0.8, 0.6, 0.4, 0.2, and 0.1, respectively.

If neither the AC nor the BC component exhibits in any part of its (zero pressure) (x, T) phase diagram the structure a, which though exists in their solid solution, then the latter is of Type III . In this case, the alloy environment stabilizes a structure which is fundamentally new to at least one of its components. Such alloy-stabilized phases with no counterpart in the phase diagram of the constituent components can be formed in bulk equilibrium growth and may be distinguished from the unusual alloy phases that are known to form in extreme non-equilibrium growth methods and in epitaxial forms. 

Mercury-cadmium-telluride is the principal semiconductor now being used in advanced infrared systems, both for military and other surveillance applications. Its preparation and use in infrared detectors and arrays was the subject of Volume 18 of this treatise. New generations of detectors and arrays require sophisticated epitaxial growth, which in turn requires precise phase diagram data. 

A schematic phase diagram of MBE growth is depicted in fig. 4 (Ohno 1998 Shen et al. 1999). Recently it was shown that metallic (Ga,Mn)As with x = 0.1 can be obtained by the use of a modified MBE growth technique at 7s = 150°C, migration-enhanced epitaxy (MEE), where the beam fluxes of source materials are precisely controlled (Sadowski et al. 2001a, 2001b). 

Liquid-Phase Epitaxy and Phase Diagrams of Compound Semiconductors... 

Several excellent reviews of liquid-phase epitaxy have appeared in the literature over the past 15 years (1-12). The discussion in this chapter will be limited in scope but will supplement the material discussed in previous reviews. In particular, issues that can be analyzed by traditional methods of chemical engineering are addressed for this chemical process. Because the growing solid-liquid interface is near equilibrium, the calculation of multicomponent compound-semiconductor phase diagrams will be emphasized. 

A primary focus of our work has been to understand the ferroelectric phase transition in thin epitaxial films of PbTiOs. It is expected that epitaxial strain effects are important in such films because of the large, anisotropic strain associated with the phase transition. Figure 8.3 shows the phase diagram for PbTiOs as a function of epitaxial strain and temperature calculated using Landau-Ginzburg-Devonshire (lgd) theory [9], Here epitaxial strain is defined as the in-plane strain imposed by the substrate, experienced by the cubic (paraelectric) phase of PbTiOs. The dashed line shows that a coherent PbTiOs film on a SrTiOs substrate experiences somewhat more than 1 % compressive epitaxial strain. Such compressive strain favors the ferroelectric PbTiOs phase having the c domain orientation, i.e. with the c (polar) axis normal to the film. From Figure 8.3 one can see that the paraelectric-ferroelectric transition temperature Tc for coherently-strained PbTiOs films on SrTiOs is predicted to be elevated by 260°C above that of... 

Figure 8.3 Phase diagram for epitaxially-strained PbTiOs calculated using Landau-Ginzburg-Devonshire theory [9]. The dashed line shows the epitaxial strain corresponding to a SrTiC>3...

Figure 8.8 Phase diagram for epitaxial PbTiOa thin films on SrTiOs. Circles no satellites, paraelectric phase P. Triangles ferroelectric stripe phase Diamonds ferroelectric stripe phase Fp. Squares ferroelectric monodomain phase If.

A number of factors can influence the behavior of ferroelectric thin films and multilayer stmctures with layer thickness at nanometer scale. One of the major factors is strain in epitaxial structures [15]. Recent demonstrations of huge strain effect on ferroelectric properties include changes in the phase diagram [16-22], dramatic enhancement of ferroelectric polarization, and increase of the ferroelectric phase transition temperature [23-27], induced ferroelectricity in non-ferroelectric materials like SrTi03 or KTa03 [28-33], or even simple rocksalt binary oxides like BaO ([34], theoretically predicted). 

Pertsev NA, Zembilgotov AG, Tagantsev AK (1998) Effect of mechanical boundary conditions on phase diagrams of epitaxial ferroelectric thin films. Phys Rev Lett 80 1988... 

Lai B-K, Kornev lA, Bellaiche L, Salamo GJ (2005) Phase diagrams of epitaxial BaTi03 ultrathin films from first principles. Appl Phys Lett 86 132904... 

The principles of the epitaxial growth can be described using the phase diagram of the binary system Si-Sn as an example (Fig. 9.1). The upper curve represents the so-called liquidus . At point A, the system is a liquid mixture of Sn solvent and Si, at temperature Ta with a composition A"a the solution is saturated with silicon. 

The maximum in catalytic activity observed for the multiphase region of the phase diagram necessarily arises from interactions between the separate phases. The bismuth rich and cerium rich solid solutions can readily form coherent interfaces at the phase boundaries due to the structural similarities between the two phases which can permit epitaxial nucleation and growth. A good lattice match exists between the [010] faces of the compounds, this match is displayed in Figure 6. We have also shown that regions of an [010] face of a Ce doped bismuth molybdate crystal resembles cerium molybdate compos tionally. This means that the interface between the two compounds need not have sharp composition gradients. It is structurally possible for the Bi-rich phase to possess a metal stiochiometry at the surface that matches that of the Ce-rich phase. 

Fig. 13. Phase diagram for K adsorption on R(lll) [88P1]. In the multiphase region a continuous compression of the overlayer results in rotational epitaxy or aligned structures.

Fig. 7. Magnetic phase diagram for epitaxial Dy thin films grown on (OOOI)Y-Lu alloys. The phase boundary intercepts the / = 0 plane along the line of strain-dqiendent Curie temperatures Tde).

Liquid phase epitaxy (LPE) is a growth method where the deposition of the Si is driven by the Si supersaturated metal melt that is cooled down from above 1,000 °C. Epitaxial growth starts according to the metal Si phase diagram in equilibrium. The melt is cooled down, and the liquid Si deposits onto the solid Si substrate. The growth rate is in the range of 0.1 and 1 pm/min. 

The phase diagram of such curved surfaces in the amphiphilic system has been studied by Huse and Liebler [8] on the basis of the elastic energy of the surface. The phase behavior is determined by the balance of the surface tension, the bending rigidity and the saddle-splay modulus of the curved interface and the IPMS structure appears when the saddle-splay modulus increased to a some critical value. Mathematically, more than 30 species of curved surfaces have been reported as IPMS [9] and, experimentally, several types of IPMS structures have been found in cubic phases of lipid-water systems [10]. Concerning the formation mechanism of the cubic network, Ranpon and Charvolin [6] found the epitaxial relationships between reticular planes of these three phases in the... 

Phillips reported that, as the pressure is increased, the proportion of y modification increases from 0 at atmospheric pressure to close to 100% at 2 kbar. It appears that the lower the supercooling the higher the amount of y modification produced at a specific pressure [65]. A model was proposed for the crystallization in which the two crystals deposit within the same lamellae through an epitaxial process. Theoretical and experimental prediction of the pure y modification as a function of temperature and pressure can be found in the phase diagram proposed by Phillips [68], see Fig. 4. 

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