Low-Field DC Transport Coefficients

Abstract

Electron transport in semiconductors is usually studied in the presence of various external forces such as electric fields with or without magnetic fields, high-frequency electromagnetic fields with or without a DC magnetic field, temperature gradients, or electron density gradients. Some of these studies are aimed at the discovery of new phenomena with possible practical applications, but a majority of them are used for characterising the materials. We shall discuss in this chapter the transport coefficients related to electron transport caused by a small DC electric field. We shall also consider the effect of a DC magnetic field. In addition we shall deal with the transport of electrons due to a density gradient and also due to a temperature gradient. The coefficients related to electron transport under these conditions are drift mobility, Hall mobility, magnetoresistance, diffusion coefficient, and thermoelectric power. By studying these various coefficients, it is possible to determine the suitability of a material for applications in a particular device. The basic electron parameters such as the effective mass and number density may also be determined from such studies. In addition the importance of various scattering mechanisms may also be estimated. To extract all this information, the theoretical values of the coefficients have to be derived accurately. The principles of the methods used for this purpose have been discussed in the preceding chapter. In this chapter, we derive formulae giving the various coefficients, and give some examples to illustrate the methods.