Upper value of thermoelectric figure of merit for isotropic semiconductors

Within the framework of two-temperature model (electron and phonon temperature) the problem of thermoelectric figure of merit in semiconductor layers is theoretically investigated. It is shown, that it reaches the maximal value in semiconductor films with thickness smaller of a cooling length. Increase of the thermoelectric figure of merit in this case is caused by "switching-off\´ of the phonon subsystem in the general process of heat conductivity due to the special boundary conditions for electron and phonon subsystems.