A SIMPLE ANALYSIS OF THE EINSTEIN RELATION IN ULTRATHIN FILMS OF NON-PARABOLIC SEMICONDUCTORS IN THE PRESENCE OF A PARALLEL MAGNETIC-FIELD

The Einstein relation is studied for the diffusivity-mobility ratio of the carriers in non-parabolic semiconductors in the presence of a par allel magnetic field at low temperatures on the basis of a new electro n dispersion law. It is found, taking Hg1-xCdxTe and In1-xGaxAsyP1-y l attice-matched to InP as examples, that the diffusivity-mobility ratio increases with increasing surface electron concentration, decreasing alloy composition and decreasing film thickness in various manners. Th e magnetic field enhances the numerical values of the diffusivity-mobi lity ratio and we suggest an experimental method of determining the Ei nstein relation in degenerate materials. In addition, the correspondin g well-known results of relatively wide gap materials in the absence o f a magnetic field are obtained as special cases of our generalized fo rmulation.