Mott-Anderson Localization in the Two-Dimensional Band Tail of Si Inversion Layers

Experimental evidence for a transition from localized to extended states in a two-dimensional band tail is obtained by measuring the conductivity in n- and p-type inversion layers in Si as a function of electron density and temperature (4.2 to 0.4^∘{}K). A transition from metallic to thermally activated conductivity is observed as a function of electron density, while the temperature dependence at electron densities below the transition shows both thermally activated nearest-neighbor hopping and variable-range hopping as proposed by Mott.