Impurity doped solid

Ions like S2, SeJ and SSe are found to align along the <110> directions in most alkali halides, while in Nal, KBr and KI, the S—bond of S2 is oriented along the <100> direction. In the case of Oj, the p orbitals are parallel to the <100> direction in sodium salts but are parallel to the direction in rubidium and potassium salts. Extensive spectroscopic studies have been reported on molecular ions such as NO, NO3, Cr04 and MnO . Several reviews(Corish et al, 1977 Bridges, 1975 Grimes, 1976) are available on such impurity-doped solids. 

The principle of laser action was first demonstrated in 1960 by Maiman. This first system was a solid-state laser a ruby crystal served as the active element, and it was pumped with a flash lamp. With this report of laser action, the main concepts upon which solid-state lasers are based became established (see Fig. 1). The idea of optically pumping the laser rod was realized, as well as the use of an impurity-doped solid as the laser medium. Lastly, the concept of a laser resonator, as adapted from the work of Townes and Schalow, was experimentally demonstrated. Much of this article is essentially an exposition of the extensive techni-... 

Optical pumping Impurity-doped solid Optical resonator... 

Doping of solid reactant involves the introduction of a controlled amount of an impurity into solid solution in the host lattice. Such impurities can be selected to cause the generation or destruction of those electronic or structural defects which participate in the rate process of interest. Thus, the influence of the additive on kinetic behaviour can provide evidence concerning the mechanism of reaction [46,47]. Even if the... 

Nonstoichiometric Compounds Intrinsic defects are stoichiometric defects (i.e., they do not involve any change in overall composition). Defects can also be nonstoichiometric. In the case of extrinsic defects where the host crystal is doped with aliovalent impurities, the solid so formed is a nonstoichiometric compound because the ratio of the atomic components is no longer the simple integer. There is also... 

The properties of semiconductors are extremely sensitive to the presence of impurities at concentrations as low as 1 part in 10 °. For this reason, silicon manufactured for transistors and other devices must be very pure. The deliberate introduction of a very low concentration of certain impurities into the very pure semiconductor, however, alters the properties in a way that has proved invaluable in constructing semiconductor devices. Such semiconductors are known as doped or extrinsic semiconductors. Consider a crystal of silicon containing boron as an impurity. Boron has one fewer valence electron than silicon. Therefore, for every silicon replaced by boron, there is an electron missing from the valence band (Figure 4.10) (i.e., positive holes occur in the valence band and these enable electrons near the top of the band to conduct electricity). Therefore, the doped solid will be a better conductor than pure silicon. A semiconductor like this doped with an element with fewer valence electrons than the bulk of the material is called a p type semiconductor because its conductivity is related to the number of positive holes (or empty electronic energy levels) produced by the impurity. 

Our first steps toward the single-molecule regime arose from work at IBM Research in the early 1980s on persistent spectral hole-burning effects in the optical transitions of impurities in solids (for a review, see [20]). Briefly, if a molecule with a strong zero-phonon transition and minimal Franck-Condon distortion is doped into a solid and cooled to liquid helium temperatures, the optical absorption becomes inhomogeneously broadened (Fig. 2.2A). The width of the lowest electronic transition for any one molecule (homogeneous width, Yjj) becomes very small because few phonons are present, while at the... 

Dipolar instabilities of impurities in solids were discovered in 1965 by Lombardo and Pohl in Li-doped KCl [49]. Since then, a large amount of off-centre and on-centre instabilities of monoatomic impurities in insulator and semiconductor materials have been reported. In many cases the impurity centres are not well characterized and the observed instabilities could be due to close defects. In this article we only consider centres with spontaneous instabilities driven by PJT mechanisms. An exhaustive review of all these centres is beyond the scope of this report and we have selected representative examples based on the authors interest. Some early reviews can be found in [93,152,153]. 

In this article experimental and theoretical work on spontaneous instabilities of impurities in solids driven by PIT vibronic coupling mechanisms is reviewed. Particular attention is paid to the results of calculations addressed to understand the microscopic origin of off-centre and on-centre instabilities and also to quantify the involved distortions. Especially, we aim to help to overcome a paradigm taken root among many researchers of physics and chemistry of solids that the instabilities of atoms and ions in pure and doped solids are due to difference of atomic sizes. On the contrary, we have presented a great quantity of experimental evidences and theoretical results showing that it is an effect of the vibronic coupling. 

The choice of impurity source and experimental setup for doping a semiconductor depends on the impurity and on factors such as vapor pressure and purity of the impurity source, solid solubility in the semiconductor, and alloying or compound formation on the semiconductor surface. 

Variety of substrate material—although virtually any material can be implanted, one must choose a material for impurity doping in solid state semiconductors which can be electrically activated. 

Tan] Tani, J.-L, Kido, H., First Princple Calculation of the Geometrical and Electronic Stmcture of Impurity-Doped (3-FeSi2 Semiconductors , J. Solid State Chem., 163, 248-252 (2002) (Calculation, Crys. Stmcture, Phys. Prop., 23)... 

Remark - An impurity in solid solution in the studied phase is also a doping agent whose presence is at the same time involuntary and uncontrolled. Consequently, the study of the effects of the impurities present in the solid phases is identical to that of the doping agents. 

Several factors detennine how efficient impurity atoms will be in altering the electronic properties of a semiconductor. For example, the size of the band gap, the shape of the energy bands near the gap and the ability of the valence electrons to screen the impurity atom are all important. The process of adding controlled impurity atoms to semiconductors is called doping. The ability to produce well defined doping levels in semiconductors is one reason for the revolutionary developments in the construction of solid-state electronic devices. 

The relatively large band gaps of silicon and germanium limit their usefulness in electrical devices. Fortunately, adding tiny amounts of other elements that have different numbers of valence electrons alters the conductive properties of these solid elements. When a specific impurity is added deliberately to a pure substance, the resulting material is said to be doped. A doped semiconductor has almost the same band stmeture as the pure material, but it has different electron nonulations in its bands. 

The two extremes of ordering in solids are perfect crystals with complete regularity and amorphous solids that have little symmetry. Most solid materials are crystalline but contain defects. Crystalline defects can profoundly alter the properties of a solid material, often in ways that have usefial applications. Doped semiconductors, described in Section 10-, are solids into which impurity defects are introduced deliberately in order to modify electrical conductivity. Gemstones are crystals containing impurities that give them their color. Sapphires and rubies are imperfect crystals of colorless AI2 O3, red. 

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