On the Theory of Metal-Insulator Transitions in Gated Semiconductors
  It is shown that recent experiments indicating a metal-insulator transition in 2D electron systems can be interpreted in terms of a simple model, in which the resistivity is controlled by scattering at charged hole traps located in the oxide layer. The gate voltage changes the number of charged traps which results in a sharp change in the resistivity. The observed exponential temperature dependence of the resistivity in the metallic phase of the transition follows from the temperature dependence of the trap occupation number. The model naturally describes the experimentally observed scaling properties of the transition and effects of magnetic and electric fields. 
Boris L. Altshuler (1) and Dmitrii L. Maslov (2) ((1) NEC Research   Institute and Princeton University, (2) University of F...