Resolving and Tuning Carrier Capture Rates at a Single Silicon Atom Gap State

TL;DR

This study investigates how carrier capture rates at a single silicon atom defect can be tuned by changing temperature and doping, using advanced microscopy techniques to measure and analyze charge transfer dynamics at the atomic level.

Contribution

It introduces a comprehensive model explaining carrier capture behavior at a single dangling bond, validated by direct measurements and microscopy techniques, revealing reservoir-dependent charge dynamics.

Findings

Carrier capture rates vary with substrate temperature, doping type, and concentration.

A unified model explains both NDR and charge transition observations.

Coulomb interactions influence the electronic features observed in STS and NDR measurements.

Abstract

We report on tuning the carrier capture events at a single dangling bond (DB) midgap state by varying the substrate temperature, doping type, and doping concentration. All-electronic time-resolved scanning tunneling microscopy (TR-STM) is employed to directly measure the carrier capture rates on the nanosecond time scale. A characteristic negative differential resistance (NDR) feature is evident in the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of DBs on both n and p-type doped samples. It is found that a common model accounts for both observations. Atom-specific Kelvin probe force microscopy (KPFM) measurements confirm the energetic position of the DB's charge transition levels, corroborating STS studies. It is shown that under different tip-induced fields the DB can be supplied from two distinct reservoirs: the bulk conduction band and/or the valence band. We measure the filling and emptying rates of the DBs in the energy regime where electrons are supplied by the bulk valence band. By adding point charges in the vicinity of a DB, Coulombic interactions are shown to shift observed STS and NDR features.