Strained layers

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... 

Fig. 3.51. RBS spectra of 2.07 MeV He ions back-scattered from a Sii-xdex/Si strained layer superlattice.

R. K. Akchurin, D. V. Komarov. Formation of multilayer strained-layer heterostructures by liquid epitaxy. I. Theoretical aspects of the problem and mathematical model. Tech Phys 42 155, 1997. 

Another concept for increasing device speed is the strained layer superlattice (SLS), which consists of alternating layers of semiconductor materials with thickness <10 nm deposited by C VD. These materials have the same crystal structure but different lattice... 

Given the lattice mismatch of InAs (a = 0.606 nm) with InSb (a = 0.648 nm), about 6.5%, defects are expected, or a strained layer superlattice at best. Figure 39 is an XRD pattern for a 41 period InAs/InSb deposit, where each period was 10 cycles of InAs followed by 10 cycles of InSb. The central [111] reflection is near 28° and is quite broad. Superlattices should display satellite peaks at angles corresponding... 

G. C. Osbourn et al., Principles and Applications of Semiconductor Strained-Layer... 

R. Hull andJ.C. Bean, Principles and Concepts of Strained-Layer Epitaxy... 

S. T. Picraux, B.L. Doyle, and J.Y. Tsao, Structure and Characterization of Strained-Layer... 

That CO chemisorption is perturbed on strained-layer Ni is not surprising in view of CO chemisorption behavior on other metal overlayer systems. For example, on Cu/Ru it has been proposed that charge transfer from Cu to Ru results in decreased occupancy of the Cu 4s level. This electronic modification makes Cu more nickel-like , and results in an increase in the binding energy... 

The catalytic activity of strained-layer Ni on W(llO) for methanation and ethane hydrogenolysis has been studied as a function of Ni coverage. The activity per Ni atom site for methanation, a structure-insensitive reaction, is independent of the Ni coverage and similar to the activity found for bulk Ni. The activation energy for this reaction is lower on the strained-metal overlayer, however, very likely reflecting the lower binding strength of CO on the bimetallic system. 

At present this may only be modelled approximately, as discussed in Chapter 4, rather than fully incorporated into the dynamical theory. This is an important cause of peak broadening in diffictrlf materials such as strained layers. 

The rapid developments in the microelectronics industry over the last three decades have motivated extensive studies in thin-film semiconductor materials and their implementation in electronic and optoelectronic devices. Semiconductor devices are made by depositing thin single-crystal layers of semiconductor material on the surface of single-crystal substrates. For instance, a common method of manufacturing an MOS (metal-oxide semiconductor) transistor involves the steps of forming a silicon nitride film on a central portion of a P-type silicon substrate. When the film and substrate lattice parameters differ by more than a trivial amount (1 to 2%), the mismatch can be accommodated by elastic strain in the layer as it grows. This is the basis of strained layer heteroepitaxy. 

Volume 33 Strained-Layer Superlattices Materials Science and Technology... 

R. Hull and J. C. Bean, Principles and Concepts of Strained-Layer Epitaxy W. J. Schaff, P. J. Tasker, M. C. Folsy, and L. F. Eastman, Device Applications of Strained-Layer Epitaxy... 

M. J. Shaw and M. Jaros, Fundamental Physics of Strained Layer GeSi Quo Vadis ... 

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