Semiconductors electronic structures

Moving around the periodic table, there are systematic variations in the diamond and zinc-blende semiconductor electronic structures. Examples of these systematic variations are shown in Table I. For Ught-element materials, like diamond, in which the distance between atoms is small, the splitting between the bonding and antibonding states is at a maximum. Going down the periodic table, such as for the series C, Si, Ge, and Sn, the elements have a larger lattice... 

Figure 1 Electron potentials related to (a) the metal and (b) the semiconductor electron structure.

K.A. Kikoin, VN. Fleurov Transition Metal Impurities in Semiconductors Electronic Structure and Physical Properties, (World Scientific, Singapore, 1994), p. 163... 

Semiconductors, Principles, Fig. 3 Key features of semiconductor electronic structure... 

Cohen M L and Cheiikowsky J R 1989 Electronic Structure and Optical Properties of Semiconductors 2nd edn (Springer)... 

STM found one of its earliest applications as a tool for probing the atomic-level structure of semiconductors. In 1983, the 7x7 reconstructed surface of Si(l 11) was observed for the first time [17] in real space all previous observations had been carried out using diffraction methods, the 7x7 structure having, in fact, only been hypothesized. By capitalizing on the spectroscopic capabilities of the technique it was also proven [18] that STM could be used to probe the electronic structure of this surface (figure B1.19.3). 

Wang L S and Wu H 1998 Probing the electronic structure of transition metal clusters from molecular to bulk-like using photoeieotron spectroscopy Cluster Materials, Advances In Metal and Semiconductor Clusters vo 4, ed M A Duncan (Greenwich JAI Press) p 299... 

These surprising results can be understood on the basis of the electronic structure of a graphene sheet which is found to be a zero gap semiconductor [177] with bonding and antibonding tt bands that are degenerate at the TsT-point (zone corner) of the hexagonal 2D Brillouin zone. The periodic boundary... 

As the nanotube diameter increases, more wave vectors become allowed for the circumferential direction, the nanotubes become more two-dimensional and the semiconducting band gap disappears, as is illustrated in Fig. 19 which shows the semiconducting band gap to be proportional to the reciprocal diameter l/dt. At a nanotube diameter of dt 3 nm (Fig. 19), the bandgap becomes comparable to thermal energies at room temperature, showing that small diameter nanotubes are needed to observe these quantum effects. Calculation of the electronic structure for two concentric nanotubes shows that pairs of concentric metal-semiconductor or semiconductor-metal nanotubes are stable [178]. 

Solid-state electronic devices such as diodes, transistors, and integrated circuits contain p-n junctions in which a p-type semiconductor is in contact with an n-type semiconductor (Fig. 3.47). The structure of a p-n junction allows an electric current to flow in only one direction. When the electrode attached to the p-type semiconductor has a negative charge, the holes in the p-type semiconductor are attracted to it, the electrons in the n-type semiconductor are attracted to the other (positive) electrode, and current does not flow. When the polarity is reversed, with the negative electrode attached to the n-type semiconductor, electrons flow from the n-type semiconductor through the p-type semiconductor toward the positive electrode. 

In this contribution it is shown that local density functional (LDF) theory accurately predicts structural and electronic properties of metallic systems (such as W and its (001) surface) and covalently bonded systems (such as graphite and the ethylene and fluorine molecules). Furthermore, electron density related quantities such as the spin density compare excellently with experiment as illustrated for the di-phenyl-picryl-hydrazyl (DPPH) radical. Finally, the capabilities of this approach are demonstrated for the bonding of Cu and Ag on a Si(lll) surface as related to their catalytic activities. Thus, LDF theory provides a unified approach to the electronic structures of metals, covalendy bonded molecules, as well as semiconductor surfaces. 

In this chapter, we develop a model of bonding that can be applied to molecules as simple as H2 or as complex as chlorophyll. We begin with a description of bonding based on the idea of overlapping atomic orbitals. We then extend the model to include the molecular shapes described in Chapter 9. Next we apply the model to molecules with double and triple bonds. Then we present variations on the orbital overlap model that encompass electrons distributed across three, four, or more atoms, including the extended systems of molecules such as chlorophyll. Finally, we show how to generalize the model to describe the electronic structures of metals and semiconductors. 

The description derived above gives useful insight into the general characteristics of the band structure in solids. In reality, band structure is far more complex than suggested by Fig. 6.16, as a result of the inclusion of three dimensions, and due to the presence of many types of orbitals that form bands. The detailed electronic structure determines the physical and chemical properties of the solids, in particular whether a solid is a conductor, semiconductor, or insulator (Fig. 6.17). 

Electrochemical reactions at semiconductor electrodes have a number of special features relative to reactions at metal electrodes these arise from the electronic structure found in the bulk and at the surface of semiconductors. The electronic structure of metals is mainly a function only of their chemical nature. That of semiconductors is also a function of other factors acceptor- or donor-type impurities present in bulk, the character of surface states (which in turn is determined largely by surface pretreatment), the action of light, and so on. Therefore, the electronic structure of semiconductors having a particular chemical composition can vary widely. This is part of the explanation for the appreciable scatter of experimental data obtained by different workers. For reproducible results one must clearly define all factors that may influence the state of the semiconductor. 

Vladimir I. Veselovsky studied the photoelectrochemical behavior of metals covered with oxide layers having semiconductor properties. In 1955, Walter H. Brattain and Charles G. B. Garrett published a paper in which they established the connection between the photoelectrochemical properties of single-crystal semiconductors and their electronic structure. 

To further substantiate the proposed model, they have carried out some investigations connected with modification of semiconductor electron subsystem [174, 175]. Temperature is one of the important factors. Having no effect on the electron emission from the metal under the action of RGMAs, temperature strongly affects the current-transfer processes at the metal - semiconductor contacts. The impact of temperature on the interaction of RGMAs with Au/ZnO structures can be evaluated as follows. 

The different types of quinones active in photosynthesis are being used as electron acceptors in solar cells. The compounds such as Fd and NADP could also be used as electron/proton acceptors in the photoelectrochemical cells. Several researchers have attempted the same approach with a combination of two or more solid-state junctions or semiconductor-electrolyte junctions using bulk materials and powders. Here, the semiconductors can be chosen to carry out either oxygen- or hydrogen-evolving photocatalysis based on the semiconductor electronic band structure. 

The electron hyperfine interaction thus has important effects on both NMR relaxation and frequency shifts, and can provide valuable information on the incorporation of magnetic ions into semiconductor lattices and the resulting electronic structure as characterized by transferred hyperfine constants. Examples in Sect. 4 will show how the possible incorporation of magnetic ions into semiconductor nanoparticles can be studied by NMR. 

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