States electronic, doped crystals

Fig. 83. (a) Schematic electronic structure of a ion in a MnOg octahedron with IT distortion. The in-plane eg band in the layered manganite shows a different band dispersion and bandwidth depending on the respective orbital states, (b) Doping-level dependence of lattice distortion at room temperature in La2 2jSr +2jMii207. Thick arrows on the right hand of respective crystal structures indicate the spin structures within a bilayer unit at low temperatures. After Kimura et al. (1998). 

In practice both natural and synthetic crystals are oxygen deficient, leading to donor levels approximately 0.1 eY below the bottom of the conduction band and consequently to n-type semiconductivity. Doping the crystal with group V elements also induces n-type semiconductivity the usual dopant is antimony. The ground state electronic configuration of the Sb atom is 5s2p3, and when it... 

The hexahalorhenate(IV) anions have been the subjects of extensive electronic absorption spectra studies. Their spectra have been recorded in aqueous and non-aqueous solvents, in halide melts, in the solid state and doped into other crystal hosts (e.g. K2PtCl[Pg.172]

Carbon electronics started from the investigation of diamond single crystals (sp -type hybridization) because the diamond crystal structure is similar to that of Si and Ge. It was expected that both p- and n-type doping could be achieved in diamond to obtain the basic element of solid-state electronics that is, the p-n junction. However, the conductivity of only the p-type was realized in diamond and it was the main obstacle to the creation of carbon electronics. Nevertheless, there is an alternative route to the creation of hetero-junctions by use of the highly oriented sp -hybridized carbon films doped by different elements. 

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... 

Finally, there are defects resulting from the presence of impurities. Some of these, when deliberately devised and controlled, constitute the basis for solid-state electronic technology.3 For example, a crystal of germanium (which has the diamond structure) can be doped with traces of either gallium or arsenic. A gallium atom can replace one of germanium but an electron vacancy is created. An electron can move into this hole, thus creating... 

Both solitons and polarons have their characteristic absorption bands below the band gap energy. Then, for the identification of the nonlinear excited states, the optical absorption and the electron spin resonance spectra must be studied, to get information about the midgap states and the spin, respectively. Studies of the electrical properties are also needed to get information about the charge. In this report, the excited states in single crystals of (Pt(en)2][Pt(en) ] 2 4 are studied by the experimental methods mentioned above, and the photo-induced excited state in this material is shown to be polarons, which are also produced by halogen-doping. 

On the basis of spectroscopic data reported on Bi " doped crystals and glasses, it can be noticed that the first excitation band clearly corresponds to the dominant absorption transition Ifom Sq to at either room or lower temperature, e.g. 4.2 K, and the nature of emission transition strongly depends on temperature. After electrons have been raised to some vibrational level of the excited state of Pi, part of them will, at lower temperatures, relax to the lower-lying Pq state by way of a nonradiative transition, and therefore the forbidden Pq So transition can be observed. However, at higher temperatures, electrons on the state of Pq, if there has ever been any electron populated on the state, will tend to be thermally depleted to P]. As a consequence, the emission due to the transition of Pi —> So preponderates. Thus, at room temperature the excitation peak in borate and silicate glasses (see column Aex of Table 14.1) is attributed to the transition of So —> Pi, and the emission to Pi Sq (see column Aem of Table 14.1) [44]... 

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