Tunable tunnel barriers in a semiconductor via ionization of individual atoms

TL;DR

This study demonstrates how individual adatoms on InSb surfaces can be used to control tunneling currents and band bending, with effects tunable by imaging conditions and extending over large distances.

Contribution

It reveals the ionization and impact tunneling effects of single adatoms on InSb, showing their potential for nanoscale electronic control.

Findings

Tunneling impact can be increased up to 100x.

Tunneling effects are tunable by bias, current, and illumination.

Ionization effects extend over distances greater than 50 nm.

Abstract

We report scanning tunneling microscopy studies of individual adatoms deposited on an InSb(110) surface. The adatoms can be reproducibly dropped off from the STM tip by voltage pulses, and impact tunneling into the surface by up to ~100x. The spatial extent and magnitude of the tunneling effect are widely tunable by imaging conditions such as bias voltage, set current and photoillumination. We attribute the effect to occupation of a (+/0) charge transition level, and switching of the associated adatom-induced band bending. The effect in STM topographic images is well reproduced by transport modeling of filling and emptying rates as a function of the tip position. STM atomic contrast and tunneling spectra are in good agreement with density functional theory calculations for In adatoms. The adatom ionization effect can extend to distances greater than 50 nm away, which we attribute to the low concentration and low binding energy of the residual donors in the undoped InSb crystal. These studies demonstrate how individual atoms can be used to sensitively control current flow in nanoscale devices.