Semiconductors crystal structure

Liquid-phase carbonization occurs for some precursors, such as pitches, which become viscous fluids before carbonization. This process has been used to produce various polycrystalline graphite blocks for steel refining and electrical discharge machining, jigs for the growth of semiconductor crystals, structural components of nuclear reactor, etc. 

Semiconductor Crystal structure Band gap (eV) Type of band gap... 

Defects or impurities in the semiconductor crystal structure create electronic states in the gap region. In the case of impurities, the valence character of the impurity determines whether the level acts as an electron donor or electron acceptor state. In doping semiconductors, impurities are deliberately used to generate either donor or... 

The empirical pseiidopotential method can be illustrated by considering a specific semiconductor such as silicon. The crystal structure of Si is diamond. The structure is shown in figure Al.3.4. The lattice vectors and basis for a primitive cell have been defined in the section on crystal structures (ATS.4.1). In Cartesian coordinates, one can write G for the diamond structure as... 

Another example of epitaxy is tin growdi on the (100) surfaces of InSb or CdTe a = 6.49 A) [14]. At room temperature, elemental tin is metallic and adopts a bet crystal structure ( white tin ) with a lattice constant of 5.83 A. However, upon deposition on either of the two above-mentioned surfaces, tin is transfonned into the diamond structure ( grey tin ) with a = 6.49 A and essentially no misfit at the interface. Furtliennore, since grey tin is a semiconductor, then a novel heterojunction material can be fabricated. It is evident that epitaxial growth can be exploited to synthesize materials with novel physical and chemical properties. 

Three common uses of RBS analysis exist quantitative depth profiling, areal concentration measurements (atoms/cm ), and crystal quality and impurity lattice site analysis. Its primary application is quantitative depth profiling of semiconductor thin films and multilayered structures. It is also used to measure contaminants and to study crystal structures, also primarily in semiconductor materials. Other applications include depth profilii of polymers, high-T superconductors, optical coatings, and catalyst particles. ... 

Epitaxy. There is often a sharp orientation relationship between a singlecrystal substrate and a thin-film deposit, depending on the crystal structures and lattice parameters of the two substances. When such a relationship exists, the deposit is said to be in epitaxy with the substrate. The simplest relationship is parallel orientation, and this is common in semiconductor heterostructures, but more complex relationships are often encountered. 

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... 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

W. B. Pearson, The crystal structures of semiconductors and a general valence rule. Acta Crystallogr. 17 (1964) 1. 

Doping is important for semiconductors in order to tune their optical and electrical properties for the potential applications in biotechnology and solar cells [65]. Ag-doped hexagonal CdS nanoparticles were successfully obtained by an ultrasound-assisted microwave synthesis method. Here, the doping of Ag in to CdS nanoparticles induced the evolution of crystal structure from cubic to hexagonal. Further support from photocatalytic experiment also clearly indicates the doping of Ag clusters into the CdS matrix. 

Since this review is oriented towards chemists who may have very little familiarity with semiconductors, Sect. 2 attempts to provide some brief useful background not otherwise readily found in one place (much more detailed exposition can be found in textbooks such as the excellent one by Yu and Cardona [15]). It begins in Sect. 2.1 with a concise introduction to some basics aspects of semiconductors relevant to understanding terminology encountered in the literature on NMR of semiconductors. The four crystal structures adopted by the majority of important semiconductors will be summarized in Sect. 2.2, and the various methods of making semiconductors will be outlined in Sect. 2.3. 

Four simple crystal structural types encompass the majority of elemental or binary semiconductors. The high symmetry of the structures has important consequences for the NMR spectra in several respects ... 

The ZB and WZ crystal structures are the most common types for binary octet semiconductors [23], and for III-V semiconductors they constitute practically the only ones known to occur. The energy differences between the two forms have been... 

The fourth and final crystal structure type common in binary semiconductors is the rock salt structure, named after NaCl but occurring in many divalent metal oxides, sulfides, selenides, and tellurides. It consists of two atom types forming separate face-centered cubic lattices. The trend from WZ or ZB structures to the rock salt structure takes place as covalent bonds become increasingly ionic [24]. 

Because the cubic ZB and hexagonal WZ crystal structures described in Sect. 2.2 are energetically very similar and differ only in their stacking sequence, in a number of semiconductors either or both forms may be present depending upon growth conditions. Figure 7 shows how MAS-NMR on nuclei of both elements in GaN can clearly distinguish the more stable WZ form from the less common ZB form. 

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