The Schottky-Mott Rule Expanded for Two-Dimensional Semiconductors: Influence of Substrate Dielectric Screening

Soohyung Park, Thorsten Schultz, Dongguen Shin, Niklas Mutz, Areej Aljarb, Hee Seong Kang, Chul Ho Lee, Lain Jong Li, Xiaomin Xu, Vincent Tung, Emil J.W. List-Kratochvil, Sylke Blumstengel, Patrick Amsalem, Norbert Koch

Research output: Contribution to journalArticlepeer-review

Abstract

A comprehensive understanding of the energy level alignment mechanisms between two-dimensional (2D) semiconductors and electrodes is currently lacking, but it is a prerequisite for tailoring the interface electronic properties to the requirements of device applications. Here, we use angle-resolved direct and inverse photoelectron spectroscopy to unravel the key factors that determine the level alignment at interfaces between a monolayer of the prototypical 2D semiconductor MoS2 and conductor, semiconductor, and insulator substrates. For substrate work function (φsub) values below 4.5 eV we find that Fermi level pinning occurs, involving electron transfer to native MoS2 gap states below the conduction band. For φsub above 4.5 eV, vacuum level alignment prevails but the charge injection barriers do not strictly follow the changes of φsub as expected from the Schottky-Mott rule. Notably, even the trends of the injection barriers for holes and electrons are different. This is caused by the band gap renormalization of monolayer MoS2 by dielectric screening, which depends on the dielectric constant (ϵr) of the substrate. Based on these observations, we introduce an expanded Schottky-Mott rule that accounts for band gap renormalization by ϵr -dependent screening and show that it can accurately predict charge injection barriers for monolayer MoS2. It is proposed that the formalism of the expanded Schottky-Mott rule should be universally applicable for 2D semiconductors, provided that material-specific experimental benchmark data are available.

Original languageEnglish
Pages (from-to)14794-14803
Number of pages10
JournalACS nano
Volume15
Issue number9
DOIs
Publication statusPublished - 2021 Sep 28

Keywords

  • 2D semiconductors
  • Fermi level pinning
  • MoSmonolayer
  • electron affinity
  • ionization energy
  • photoelectron spectroscopy

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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