ON THE EINSTEIN RELATION IN ULTRATHIN FILMS OF IV-VI COMPOUNDS IN THEPRESENCE OF A PARALLEL MAGNETIC-FIELD

We have studied the Einstein relation for the diffusivity-mobility rat io of carriers in ultrathin films of IV-VI compounds in the presence o f a parallel magnetic field at low temperatures on the basis of a new 2D electron dispersion law. It is found, taking ultrathin films of PbS , PbSe, and PbTe as examples, that the diffusivity-mobility ratio incr eases with increasing electron concentration and decreasing film thick ness in various oscillatory manners. The magnetic field and the quantu m wire structure enhance the numerical values of the same ratio. We ha ve suggested an experimental method of determining the Einstein relati on in degenerate materials having arbitrary dispersion laws from the m easurement of thermoelectric power in the presence of a large magnetic field. In addition, the corresponding well-known results for relative ly wide-gap quantum confined materials in the absence of the magnetic field have been obtained as special cases of our generalized formulati ons, under certain limiting conditions.