Electron transport phenomena in small-gap semiconductors

Abstract Electron transport phenomena in small-gap III–V, II–VI and IV–VI semiconducting compounds are reviewed. We emphasize peculiarities due to nonparabolic energy-momentum dependence in the conduction band and the structure of Bloch wavefunctions, when electron energy becomes comparable to that of the gap. General theoretical framework is compared with real conduction bands in the materials of interest. Thermodynamic properties of electron gas are derived for arbitrary nonparabolic and nonspherical energy bands. We develop a theory of d.c. transport phenomena and free-carrier optics based on a linear Boltzmann equation solved for an ellipsoidal band of arbitrary nonparabolicity. Elastic electron scattering is considered taking into account true Bloch eigenstates of the conduction electrons. We give a unified description of electron mobility, thermoelectric power, thermomagnetic phenomena and free-carrier optical effects illustrating the theoretical methods with experimental results of various authors. It is demonstrated that the energy band structure of small-gap semiconductors must be consistently used in the realistic description of their transport properties.