Electronegative dopant

FIGURE 14.1 Energy levels using the phenomenological shell model for spherical clusters (a) homogeneous background potential, (b) electronegative dopant atom in the center, and (c) electropositive dopant atom in the center. 

In order for dopant atoms to be stabilized within a host lattice, both types of atoms must have similar electronegativities. If this prerequisite were not met, electron density would transfer to the more electronegative atoms, forming a compound between lattice and dopant atoms. For instance, the exposure of an iron lattice to chlorine gas would result in a yellow compound of FeCls instead of reddish crystals of Cl-doped iron. 

Silicon is normally the first material that comes to mind when speaking of semiconductors, but silicon is, in fact, not an intrinsic semiconductor. Solid silicon must be doped to become a semiconductor. Doping is the process of adding a miniscule amount of impurity to a solid such as silicon. Two of the favorite dopants for silicon are phosphorus and aluminum because they are on either side of silicon on the periodic table. They have about the same size and electronegativity, so they can easily fit next to silicon in a solid. They change the conductive properties of silicon because they have, respectively, one more and one fewer electron than silicon. 

Solid Solutions Electronegativity Ionic-Covalent Dopant States Impurity States Trapping States Valence Bands... 

It was next found that modification of the ionicity of the Ce-S bond could be achieved by incorporating dopants in the cationic lattice vacancies. The color of Ce3 xS4 doped with alkali cations (Li, K, Na) could thus be tuned from red (Eg=1.9 eV) to orange (Eg= 2.1 eV), depending on the nature and the amount of dopant used. This phenomenon was attributed to an increase of ionicity of the Ce-S bond due to the lower electronegativity of the alkali cation, compared to that of Ce T... 

Cation doping of fluorides always leads to a crystal structure distortion. The degree of distortion depends on the size ratio and properties (in the first place, electronic structure and electronegativity) of dopant and matrix cations as well as on the replacement type isovalent or heterovalent replacement. 

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