Disorder, electron-electron interactions and the metal-insulator transition in heavily doped Si:P

Abstract

Electron localization in a metal, ultimately leading to a metal-insulator (MI) transition, can occur because of disorder (Anderson transition) or electron-electron interactions (Mott-Hubbard transition). Both effects play a role in heavily doped semiconductors which have become prototype systems for the study of MI transitions. In this review we focus on phosphorus-doped Si. The statistical distribution of donor atoms on an atomic scale as the origin of random disorder can be checked by scanning tunneling microscopy. Long-range Coulomb interactions lead to Altshuler-Aronov corrections to the density of states N(E F) at the Fermi level and the electrical conductivity σ(T) on the metallic side of the MI transition, and to a soft Coulomb gap at E F and Efros-Shklovskii variable-range hopping on the insulating side. On-site Coulomb interactions, on the other hand, lead to the formation of localized magnetic moments and the Kondo effect on the metallic side, and to a Hubbard splitting of the donor band on the insulating side. The MI transition in Si:P can be tuned by varying the P concentration or—for barely insulating samples—by application of uniaxial stress S. The continuous stress tuning allows the observation of dynamic scaling of σ(T, S) and hence a reliable determination of the critical exponent μ of the extrapolated zero-temperature conductivity σ(0)∼|S—S c |μ, i.e.μ=1, and of the dynamical exponent z=3.KeywordsThermoelectric PowerQuantum Phase TransitionUniaxial StressLocalize MomentLocalize Magnetic MomentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.