. The Bell System technical journal . the currentinto ionic, electronic, and mixed conductors. Chlorides such as NaCl andsome sulphides are ionic semiconductors; other sulphides and a few oxides PROPERTIES AND USES OF THERMISTORS 179 such as uranium oiide are mixed semiconductors; electronic semiconductorsinclude most oxides such as MnsOs, FejOs, NiO, carbides such as siliconcarbide, and elements such as boron, silicon, germanium and ionic and mixed conductors, ions are transported through the changes the density of carriers in various regions, and thus changesthe condu
. The Bell System technical journal . the currentinto ionic, electronic, and mixed conductors. Chlorides such as NaCl andsome sulphides are ionic semiconductors; other sulphides and a few oxides PROPERTIES AND USES OF THERMISTORS 179 such as uranium oiide are mixed semiconductors; electronic semiconductorsinclude most oxides such as MnsOs, FejOs, NiO, carbides such as siliconcarbide, and elements such as boron, silicon, germanium and ionic and mixed conductors, ions are transported through the changes the density of carriers in various regions, and thus changesthe conductivity. Because this is undesirable, they are rarely used in mak-ing thermistors, and hence we will concentrate our interest on electronicsemiconductors. The theoretical and experimental physicists have established that thereare two types of electronic semiconductors which can be called N and Ptype, depending upon whether the carriers are negative electrons or areequivalent to positive holes in the filled energy band. In N type, the. ACCEPTORM PURITIES INTRINSIC Fig. 6.—Schematic energy level diagrams illustrating intrinsic, N and P types of semi-conductors. carriers are deflected by a magnetic field as negatively charged particleswould be and conversely for P type. The direction of deflections is ascer-tained by measurement of the sign of the Hall effect. The direction of thethermoelectric effect also fixes the sign of the carriers. By determiningthe resistivity, Hall coefficient and power of a particularspecimen at a particular temperature it is possible to determine the densityof carriers, whether they are negative or positive, and their mobility or meanfree path. The mobility is the mean drift velocity in a field of one volt percentimeter. The existence of these classifications is explained by the theoretical physi-cist^. 3,4 j^ terms of the diagrams in Fig. 6. In an intrinsic semiconductorat low temperatures the valence electrons completely fill all the
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