Black Phosphorus n-type doping by Cu: a microscopic surface investigation

TL;DR

This study investigates how copper doping affects black phosphorus at the microscopic level, revealing short-range n-type doping effects and Coulomb blockade phenomena through STM/STS and simulations, advancing the understanding of doping mechanisms.

Contribution

It provides the first detailed microscopic analysis of copper-induced n-type doping in black phosphorus using STM/STS and first-principles simulations.

Findings

Copper induces short-range n-type doping in black phosphorus.

Coulomb blockade phenomena observed at copper islands.

Cluster size influences doping effectiveness.

Abstract

We study surface charge transfer doping of exfoliated black phosphorus (bP) flakes by copper using scanning tunneling microscopy (STM) and spectroscopy (STS) at room temperature. The tunneling spectra reveal a gap in correspondence of Cu islands, which is attributed to Coulomb blockade phenomena. Moreover, using line spectroscopic measurements across small copper islands, we exploit the potential of the local investigation, showing that the n-type doping effect of copper on bP is short-ranged. These experimental results are substantiated by first-principles simulations, which quantify the role of cluster size for an effective n-type doping of bP and explain the Coulomb blockade by an electronic decoupling of the topmost bP layer from the underlying layers driven by the copper cluster. Our results provide novel understanding, difficult to retrieve by transport measurements, of the doping of bP by copper, which appears promising for the implementation of ultra-sharp p-n junctions in bP.