Effect of quantum confinement on impurity hopping in quantum wells

The problem of evaluation of the impurity hopping conductance in quantum wells is discussed, taking account of the impurity position-dependent shifts of the binding energies and the variation of the localization radii. It is demonstrated that these effects give rise to a temperature dependence of the conductance of the form sigma = sigma(o) exp {-(T-o/T)(1/3)}, where the parameter T-o depends on the well width L. Numerical calculations using the variational principle show that this dependence is strong far strongly compensated samples in the region of L/alpha* less than or equal to 1, where alpha* is the effective Bohr radius.