Lattice mismatch substrate

Heterocyclic sulfides, 23 645 Heteroepitaxial layers, for compound semiconductors, 22 145 Heteroepitaxy, on lattice mismatched substrates, 22 160 Heterofullerenes, 12 231—232 chemistry of, 12 252—253 Heterogeneous azeotropic distillation, 8 819-845... 

Experimentally, we can introduce a built-in strain in an epitaxial layer by growing it on a lattice mismatched substrate. As long as the mismatched epitaxial layer is below the critical thickness, the produced strain is uniform and no dislocations are induced. As a result, the in-plane lattice constant of the epitaxial layer is fitted to that of the substrate, and the out-of plane lattice constant is adjusted to a new lattice constant according to the Hook law. Then, the subband structure is modified by introducing a built-in strain, and the strain has a dramatic influence on the electronic properties of the system. Theoretically, we can easily include the strain effect in the k.p theory. 

A thermodynamic model for the molecular beam epitaxy of strained quaternary in-III -V-V layers on a lattice-mismatch substrate is developed. On the basis of the model, the In incorporation in growing GaInNAs/GaAs nanolayers is analyzed. The In concentration is calculated versus such growth parameters as the growth temperature, the growth rate, the arsenic incident flux, and the In concentration in the layer. 

Fig. 9.7. The figure shows a time sequence of surface profiles of h x, t) versus x for a strained film with a constant deposition flux onto a lattice-mismatched substrate. All the dimensions are in nanometers. The insets in (a)-(c) show the evolution of the third island from the right. To aid in the comparison of shapes at different times, the island shape from (a) has been included in (b). Similarly, the island shapes from (a) and (b) in (c). The slope of the largest island in each of the smaller insets is indicated.

Metalorganic Vapor Phase Epitaxial Growth of Nonpolar Al(Ga,ln)N Films on Lattice-Mismatched Substrates... 

In this section, as examples of nonpolar GaN on lattice-mismatched substrates, the surface morphology and microstructure of a-plane GaN on an r-plane sapphire substrate and m-plane GaN on m-plane 4H-SiC are presented. Next, the SELO method of reducing threading-dislocation and stacking-fault densities is described in detail. This is followed by a description of the properties of the conductivity control of n-type andp-type nonpolar GaN, and the growth of the heterostructure/quantum well structure. Finally, the performances of the violet and green LEDs on nonpolar GaN are discussed with respect to the threading-dislocation density dependence of the output power. 

As described previously, the most serious problem of nonpolar/semipolar GaN films on lattice-mismatched substrates is that the films contain many defects. 

RBS and channeling are extremely useful for characterization of epitaxial layers. An example is the analysis of a Sii-j Gejc/Si strained layer superlattice [3.131]. Four pairs of layers, each approximately 40 nm thick, were grown by MBE on a <100> Si substrate. Because of the lattice mismatch between Sii-jcGe c (x a 0.2) and Si, the Sii-j Ge c layers are strained. Figure 3.51 shows RBS spectra obtained in random and channeling directions. The four pairs of layers are clearly seen in both the Ge and Si... 

Similarly, the (111) GaAs substrate could be used to achieve epitaxial growth of zinc blende CdSe by electrodeposition from the standard acidic aqueous solution [7]. It was shown that the large lattice mismatch between CdSe and GaAs (7.4%) is accommodated mainly by interfacial dislocations and results in the formation of a high density of twins or stacking faults in the CdSe structure. Epitaxy declined rapidly on increasing the layer thickness or when the experimental parameters were not optimal. 

A variety of compound semiconductors have been successfully prepared by this technique. Much of the work concerning ECALE has been concentrated on the deposition of CdTe on An substrates. Notwithstanding the inherent problems of the system (for instance, a 10% lattice mismatch), the formation of CdTe epitaxial layers became a model example of ECALE synthesis. In their pioneering studies, Stickney and co-workers [27, 28] have focused on the deposition of the compound on... 

Some materials have a small lattice mismatch with the substrate, less then 1%, and can adopt the same lattice constants at the interface. This, however, still results in some strain, which builds until released, forming slip dislocations etc.. The thickness at which defects occur is of considerable interest and referred to as the critical thickness [14, 15]. Strain can be minimized by adjusting the lattice constants of the... 

There are many deposit-substrate combinations where the basic lattice mismatch is very large, such as when a compound is formed on an elemental substrate, but where excessive strain does not necessarily result. Frequently a non one-to-one lattice match can be formed. If a material can match up every two or three substrate surface unit cells, it may still form a reasonable film [16]. In many cases the depositing lattices are rotated from the substrate unit cells, as well. In a strict definition of epitaxy, these may not be considered, however, it is not clear why high quality devices and materials could not be formed. 

Studies of UPD are important for a number of reasons, most importantly, because they are the formation of the first atomic layer in an electrodeposit. In the present text, they are important because they illuminate the structures of electro-deposited atomic layers, the reactants in EC-ALE. However, such studies must be kept in context, given that the structures of the first UPD layers on a substrate generally have little to do with the structures of subsequently formed compound mono-layers. It has been found that the structures of compound monolayers are determined, for the most part, by the structure of the compound that is forming, perturbed by the lattice mismatch between the deposit and the substrate. The structure of the first atomic layer on the substrate does not appear to be a significant factor in determining... 

There are several ways to prepare thin films for use as model catalyst supports.30-31 For the purposes of this review, we will point the reader toward other sources that discuss two of these methods direct oxidation of a parent metal and selective oxidation of one component of a binary alloy. 32 34 The remaining method consists of the deposition and oxidation of a metal on a refractory metal substrate. This method has been used extensively in our group323131 11 and by others33-52-68 and will be the focus of the discussion here. The choice of the metal substrate is important, as lattice mismatch between the film and the substrate will determine the level of crystallinity achieved during film growth. 

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