Semiconductors chemical doping

Preliminary measurements of electrical conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10 °S/cm which apparently is not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase in conductivity. Ongoing studies of the electrical properties of these conjugated polymers with alternating aromatic/quinonoid units will be reported elsewhere. 

The silver(I) complexes with the tetrakis(methylthio)tetrathiafulvalene ligand have been reported, the nitrate salt presents a 3D structure with an unprecedented 4.16-net porous inorganic layer of silver nitrate,1160 the triflate salt presents a two interwoven polymeric chain structure.1161 The latter behaves as a semiconductor when doped with iodine. With a similar ligand, 2,5-bis-(5,5,-bis(methylthio)-l,3,-dithiol-2 -ylidene)-l,3,4,6-tetrathiapentalene, a 3D supramolecular network is constructed via coordination bonds and S"-S contacts. The iodine-doped compound is highly conductive.1162 (Methylthio)methyl-substituted calix[4]arenes have been used as silver-selective chemically modified field effect transistors and as potential extractants for Ag1.1163,1164... 

Doping effects have also been observed for (almost) hydrogen-free a-Si films prepared by vacuum evaporation (Beyer et al, 1979a) and by pyrolytic chemical vapor deposition (Hirose, 1981), as well as for a-Si films containing oxygen (Beyer, 1979) and fluorine (Matsumura et al, 1980). For other amorphous semiconductors successful doping has also been reported, as,... 

The limited number of pages of this Handbook has forced us, furthermore, to be even more restrictive with regard to the properties of semiconductors, which are considered as being of first-order importance for this data collection. So, semiconductor chemistry is beyond the scope of this Handbook. The very broad and inportant field of semiconductor technology could not be included at all. Also, the wide field of the influence of chemical doping, impurities, and defects on the properties of semiconductors had to be left out. The Handbook s emphasis is on the physical properties of a restricted number of most important pure semiconducting materials. 

The n-type semiconductors are doped intrinsic semiconductors in which the dopant is a pentavalent element, for instance chemical elements of group VA(15) of the periodic chart such as arsenic (As), antimony (Sb), or phosphorus (P). The substitutional impurities will give a supplementary electron owing to their ns np electronic configuration containing five rather than four outer-shell electrons. Therefore, the density of holes in the valence band is exceeded by the density of electrons in the conduction band. A hole is a mobile electron vacancy in a semiconductor that acts like a positive electron charge with a positive mass. Then, the n-type behavior is induced by doping with the addition of pentavalent element... 

Polyacetylene, a one-dimensional, conjugated polymer represented as (CH) exhibits electrical conduction upon chemical doping with an electron acceptor or donor [1,2]. The chemical doping transforms the polyacetylene from insulator or semiconductor to conductor. Ordinary polyacetylene film is composed of fibrils that are bundles of polyene chains. Because the fibrils are randomly oriented, the inherent electrical conductivity of the polyacetylene chain is depressed owing to fibril contact resistance. This makes it difficult for polyacetylene to become a complete one-dimensional conductor at the macroscopic level. Today, the primary concern is how to align the fibrils of polyacetylene film in order to achieve higher electrical conductivity. 

Electrical conduction through hopping transport is present in many highly disordered materials, such as chemically doped conductive polymers and heavily doped Si and Ge semiconductors [19]. In hopping transport, the mobility of the carriers is determined by the phonon density and thus the background temperature of the material. For a carrier to hop from one localized defect state to another, in a different location tunneling transfer must be stimulated by the inelastic scattering of a phonon. If the defect states are isotropically distributed, the carriers are not spatially limited, and three-dimensional hop processes will occur. However, if there is a one-dimensional network of defect states, a trail or path for carriers, the hop process will also be one-dimensional. 

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