Coulomb Gap in a Doped Semiconductor near the Metal-Insulator Transition: Tunneling Experiment and Scaling Ansatz

Electron tunneling experiments are used to probe Coulomb correlation effects in the single-particle density-of-states (DOS) of boron-doped silicon crystals near the critical density nc of the metal-insulator transition (MIT). At low energies (ε ≤ 0.5 meV), a DOS measurement distinguishes between insulating and metallic samples with densities 10 to 15 % on either side of nc. However, at higher energies (∼ 1 meV ≤ ε ≤ 50 meV) the DOS of both insulators and metals show a common behavior, increasing with energy as ǫm where m is roughly 0.5. The observed characteristics of the DOS can be understood using a classical treatment of Coulomb interactions combined with a phenomenological scaling ansatz to describe the length-scale dependence of the dielectric constant as the MIT is approached from the insulating side. 71.23.-k, 71.30.+h, 71.45.Gm Typeset using REVTEX