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Electrical control of anisotropic and tightly bound excitons in bilayer phosphorene

Sangho Yoon1,2,*, Taeho Kim1,2,*, Seung-Young Seo1,2, Seung-Hyun Shin3, Su-Beom Song1,2, B. J. Kim2,3, Kenji Watanabe4, Takashi Taniguchi5, Gil-Ho Lee3 et al.

Moon-Ho Jo1,2, Diana Y. Qiu6,†, and Jonghwan Kim1,2,3,‡

  • 1Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Republic of Korea
  • 2Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang, Republic of Korea
  • 3Department of Physics, Pohang University of Science and Technology, Pohang, Republic of Korea
  • 4Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
  • 5International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
  • 6Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520-8292, USA

  • *These authors contributed equally to this work.
  • †Corresponding author: diana.qiu@yale.edu
  • ‡Corresponding author: jonghwankim@postech.ac.kr
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Phys. Rev. B 103, L041407 – Published 27 January, 2021

DOI: https://doi.org/10.1103/PhysRevB.103.L041407

Abstract

Monolayer and few-layer phosphorene are anisotropic quasi-two-dimensional (quasi-2D) van der Waals (vdW) semiconductors with the linear-dichroic light-matter interaction and the widely tunable direct band gap in the infrared frequency range. Despite recent theoretical predictions of strongly bound excitons with unique properties, it remains experimentally challenging to probe excitonic quasiparticles due to the severe oxidation that occurs during device fabrication. In this study, we report the observation of strongly bound excitons and trions with highly anisotropic optical properties in intrinsic bilayer phosphorene, which are protected from oxidation by encapsulation with hexagonal boron nitride (hBN) in a field-effect transistor (FET) geometry. Reflection contrast and photoluminescence spectroscopy clearly reveal the linear-dichroic optical spectra from anisotropic excitons and trions in the hBN-encapsulated bilayer phosphorene. The optical resonances from the exciton Rydberg series indicate that the neutral exciton binding energy is over 100 meV even with the dielectric screening from hBN. The electrostatic injection of free holes enables an additional optical resonance from a positive trion (charged exciton) ∼30 meV below the optical band gap of the charge-neutral system. Our work shows exciting possibilities for monolayer and few-layer phosphorene as a platform to explore many-body physics and photonics and optoelectronics based on strongly bound excitons with twofold anisotropy.

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Phys. Rev. B 103, L041407– Published 27 January, 2021
  • Received 21 August 2020
  • Revised 15 December 2020
  • Accepted 22 December 2020
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