Electron-electron interactions and the metal-insulator transition in heavily doped silicon

The metal‐insulator (MI) transition in Si:P can be tuned by varying the P concentration or – for barely insulating samples – by application of uniaxial stress S. On‐site Coulomb interactions 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. Continuous stress tuning allows the observation of finite‐temperature 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 ‐ Sc |μ, i.e., μ = 1, and of the dynamical exponent z = 3. The issue of half‐filling vs. away from half‐filling of the donor band (i.e., uncompensated vs. compensated semiconductors) is discussed in detail. The metal‐insulator (MI) transition in Si:P can be tuned by varying the P concentration or – for barely insulating samples – by application of uniaxial stress S. On‐site Coulomb interactions 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.