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

TL;DR

This study uses tunneling experiments to investigate Coulomb correlation effects in boron-doped silicon near the metal-insulator transition, revealing a Coulomb gap and a universal high-energy DOS behavior.

Contribution

It introduces a scaling ansatz combined with Coulomb interaction theory to explain the DOS behavior near the MIT in doped semiconductors.

Findings

Coulomb gap observed in the DOS distinguishes insulating and metallic samples.

At higher energies, DOS increases as the square root of energy for both phases.

A classical Coulomb interaction model with a scaling approach explains the experimental results.

Abstract

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 of the metal-insulator transition (MIT). At low energies, a DOS measurement distinguishes between insulating and metallic samples with densities 10 to 15 % on either side of the MIT. However, at higher energies the DOS of both insulators and metals show a common behavior, increasing roughly as the square-root of energy. 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.