Electrostatic effects and band-bending in doped topological insulators

TL;DR

This paper models electrostatic effects in doped topological insulators, revealing how doping, surface charges, and external potentials influence band bending, carrier distribution, and spin-orbit coupling, with implications for thin film properties.

Contribution

It introduces a self-consistent scheme for an interacting tight binding model to analyze electrostatic effects and band bending in doped topological insulators, including the impact of surface dopants and gate potentials.

Findings

Electron and hole doping produce similar magnitude but opposite sign band bending.

Surface dopants break electron-hole symmetry, affecting band bending magnitude.

Substrate potentials can induce Rashba spin-orbit coupling in thin films.

Abstract

We investigate the electrostatic effects in doped topological insulators by developing a self consistent scheme for an interacting tight binding model. The presence of bulk carriers, in addition to surface electrons, generates an intrinsic inhomogeneous charge density in the vicinity of the surface and, as a result, band bending effects are present. We find that electron doping and hole doping produce band bending effects of similar magnitude and opposite signs. The presence of additional surface dopants breaks this approximate electron-hole symmetry and dramatically affects the magnitude of the band bending. Applying a gate potential can generate a depletion zone characterized by a vanishing carrier density. We find that the density profile in the transition zone between the depleted region and the bulk is independent of the applied potential. In thin films the electrostatic effects are strongly dependent on the carrier charge density. In addition, we find that substrate induced potentials can generate a Rashba type spin-orbit coupling in ultra thin topological insulator films. We calculate the profiles of bulk and surface states in topological insulator films and identify the conditions corresponding to both types of states being localized within the same region in space.