Superlattices of semiconductor

A new chapter in the uses of semiconductors arrived with a theoretical paper by two physicists working at IBM s research laboratory in New York State, L. Esaki (a Japanese immigrant who has since returned to Japan) and R. Tsu (Esaki and Tsu 1970). They predicted that in a fine multilayer structure of two distinct semiconductors (or of a semiconductor and an insulator) tunnelling between quantum wells becomes important and a superlattice with minibands and mini (energy) gaps is formed. Three years later, Esaki and Tsu proved their concept experimentally. Another name used for such a superlattice is confined heterostructure . This concept was to prove so fruitful in the emerging field of optoelectronics (the merging of optics with electronics) that a Nobel Prize followed in due course. The central application of these superlattices eventually turned out to be a tunable laser. 

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... 

Generation of nanoparticles under Langmuir monolayers and within LB films arose from earlier efforts to form nanoparticles within reverse micelles, microemulsions, and vesicles [89]. Semiconductor nanoparticles formed in surfactant media have been explored as photocatalytic systems [90]. One motivation for placing nanoparticles within the organic matrix of a LB film is to construct a superlattice of nanoparticles such that the optical properties of the nanoparticles associated with quantum confinement are preserved. If mono-layers of capped nanoparticles are transferred, a nanoparticle superlattice can be con-... 

Isotope superlattices of nonpolar semiconductors gave an insight on how the coherent optical phonon wavepackets are created [49]. High-order coherent confined optical phonons were observed in 70Ge/74Ge isotope superlattices. Comparison with the calculated spectrum based on a planar force-constant model and a bond polarizability approach indicated that the coherent phonon amplitudes are determined solely by the degree of the atomic displacement, and that only the Raman active odd-number-order modes are observable. 

Superlattices result from the periodic infinite repetition of heterostructures. MBE-grown superlattices of III-V semiconductors exhibit sharp interfaces and high carrier mobilities of the resulting 2D carrier gas at low temperature (Ando et al, 1982). To date no superconductivity has been found for such engineered solids, although some expectations were raised in 2000 after some reports on the obten-tion of superconductivity in semiconductor/insulator interfaces by field-induced... 

Intermixing. In some fabrication sequences it is desirable to cause the interdiffusion of semiconductor superlattices. This effect causes a... 

Redl, F. X., Cho, K. S., Murray, C. B. O Brien, S. Three-dimensional binary superlattices of magnetic nanocrystals and semiconductor quantum dots. Nature (London) 423, 968—971 (2003). 

Abstract. We describe the state-of-the-art in the creation of ordered superlattices of adsorbed atoms, molecules, semiconductor quantum dots, and metallic islands, by means of self-assembly during atomic-beam growth on single crystal surfaces. These surfaces often have long-period reconstructions or strain relief patterns which are used as template for heterogeneous nucleation. However, repulsive adsorbate-adsorbate interactions may also stabilize ordered superlattices, and vertical correlations of growth sequences of buried islands will be discussed in the case of semiconductor quantum dots. We also present new template surfaces considered as particularly promising for the creation of novel island superlattices. 

The last example we would like to discuss is a lattice of holes formed in stoichiometric hexagonal (h) BN double layers on Rh(lll), see Fig. 5(c) and [99]. The lattice is composed of holes in the BN-bilayer with a diameter of 24 2 A, and an average distance of 32 2 A. The holes in the upper layer are offset with respect to the smaller holes in the lower layer. We note that well-ordered superstructures with a large period have already been observed some time ago by means of LEED for borazine adsorption onto Re(0001) [102], while borazine adsorption onto other close-packed metal surfaces, such as Pt(lll), Pd(lll), and Ni(lll), leads to the self-limiting growth of commensurate ABN monolayers [103,104]. For BN/Rh(lll) it is not clear at present whether the Rh(lll) substrate is exposed at the bottom of the holes. If this was the case the surface would not only be periodic in morphology but also in chemistry, and therefore would constitute a very useful template for the growth of ordered superlattices of metals, semiconductors, and molecules. 

G. C. Osbourn etal., Principles and Applications of Semiconductor Strained-Layer Superlattices... 

The more traditional approach has already been used in anodic electrocrystallization processes to produce nanocompositions and superlattices of mixed Ti-Pb oxides [341-347]. With HTSC materials, initial steps have been made in this direction in studies on the electrochemical deposition of conductive polymers on the surface of microband YBCO electrodes [28,50,433]. In the resulting composition, the reversible transition from the HTSC/metal junction (at the high doping degree of the polymer) to the HTSC/semiconductor junction has been achieved. The properties of these compositions allow one to control the shift over a wide interval. 

Jaros M. (1989b), Quantum wells, superlattices, quantum wires, and dots , in Physics and Applications of Semiconductor Micro structures, Oxford University Press, New York, pp. 83-106. 

In conclusion of this section one may say that the linear optics of superlattices bear rich information on the dynamics of interfaces. Such investigations may give an idea of the nature of the interaction of bulk excitations (excitons) with interfaces which manifests itself in additional boundary conditions (ABC) and determines the value of the constant a. Finally, the study of dispersion laws for polaritons in superlattices with semiconductor layer thicknesses small in comparison with the Bohr radius of exciton permits one to follow variations in the properties of excitons. 

S.E. Saddow, M. Mynbaeva, and M. MacMillan, Chapter 8 Porous SiC technology , in Silicon Carbide Materials, Devices and Applications, Zhe Chuan Feng and Jian H. Zhao (Eds), Optoelectronic Properties of Semiconductors and Superlattices, Taylor and Francis Engineering, New York, 2003. 

A. Amann, J. Schlesner, A. Wacker, and E. Scholl Self-generated chaotic dynamics of field domains in superlattices, in Proc. 26th International Conference on the Physics of Semiconductors (ICPS-26), Edinburgh 2002, edited by J. H. Davies and A. R. Long (2003). 

The study of metal adatoms deposited onto the surface of semiconductor electrodes is of interest for electrodeposition of epitaxial [1] and textured [2] films and superlattices of metal chalcogenides [3]. In the past decade, an additional interest in processes of underpotential deposition (upd) has been stimulated by the progress in studying physics and chemistry of nanosize objects [4]. 

There Is an additional element which appears In the case of the T1 superconductors which may be worthy of note and further speculation. We first recall that some years ago, Allender, Bray, and Bardeen (32) (ABB) proposed a specific excltonlc mechanism of superconductivity employing a model of semiconductor-metal Interfaces. In the ABB model, the metallic electrons at the Fermi energy tunnel Into the semiconductor and Cooper pair by exchanging virtual "excltons", l.e., virtual electron-hole pairs. As discussed above, the pDOS structure of Tl/2212 and Tl/2223 shows that both systems can be viewed as a metal-semiconductor (or metal-semlmetal) superlattice structure, where the CUO2 metal layers provide conduction electrons and the Tl-03-02 layers serve as low-gap semiconductors. Since the T1 s (d 2 nd 02, 03 P2 states are covalently hybridized, a virtual elicitation from the non-bonding Px,y states of 02 and 03 to the anti-bonding T1 s (d Pz state may... 

Lead Chalcogenides, in Optoelectronic Properties of Semiconductors and Superlattices, Vol. 18, Taylor Francis Inc., 2003 R 228 T. Story, Semimagnetic Semiconductors Based on Lead Chalcogenides ,... 

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