Compensation independence of anomalous metal-semiconductor tunneling near the Mott transition

A temperature-dependent minimum in the conductance dIdV=G(V) is observed in tunneling into compensated Si:Sb near the metallic transition which, unexpectedly, does not shift from V=0 for substantial compensation K=NAND. A temperature dependence G(0)exp(- BT14) is observed below 4.2 K in nonmetallic samples, which indicates variable-range assisted tunneling into localized states. These results discriminate against a direct density-of-states interpretation of the conductance minimum. It is suggested that the effective electron-phonon coupling indicated by G(0)exp(- BT14) at V=0 enables an electron injected with energy eVkT, but still in the range of Anderson localization, to emit phonons and thus reach final states in the energy range 0<E<e V, relative to the Fermi energy. One may thus expect G(e V)0eVN(E) dE, consistent with G(0) a minimum, independent of K, as observed.