Theory of thermopower in disordered mixed crystals: Application to Si-Ge systems

A Green's-function theory of thermoelectric power in disordered mixed crystals is presented. This theory incorporates features of (a) disorder, (b) band structure, (c) relevant dielectric function, and (d) electron-phonon interaction. By formulating the theory in coordinate space, besides subsuming previous work on metals and alloys as special cases, the inclusion of disorder effects based on coherent potential approximation has been incorporated into this scheme. This formulation gives the concentration and band occupancy dependence of thermopower. Thus it provides a possibility for investigating other disordered mixed systems which may be tailored to yield larger values of thermoelectric figure of merit. As an illustration of this formalism, numerical estimations of the contributions due to disorder and electron-phonon effects to the thermopower in a two-band model of Si-Ge mixed crystal system are given at room temperature. [S0163-1829(99)00441-5].