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Localized excitons in defective monolayer germanium selenide

Journal Article · · Physical Review Materials
 [1];  [2];  [2];  [2]
  1. Boston Univ., MA (United States); Boston University
  2. Boston Univ., MA (United States)
+ Show Author Affiliations
Germanium selenide (GeSe) is a van der Waals–bonded layered material with promising optoelectronic properties, which has been experimentally synthesized for two-dimensional (2D) semiconductor applications. In the monolayer, due to reduced dimensionality and, thus, screening environment, perturbations such as the presence of defects have a significant impact on its properties. We apply density functional theory and many-body perturbation theory to understand the electronic and optical properties of GeSe containing a single selenium vacancy in the –2 charge state. We predict that the vacancy results in midgap “trap states” that strongly localize the electron and hole density and lead to sharp, low-energy optical absorption peaks below the predicted pristine optical gap. Analysis of the exciton wave function reveals that the 2D Wannier-Mott exciton of the pristine material monolayer is strongly modified by the presence of the defect. The lowest-energy exciton wave function is highly localized around the defect, with the Bohr radius reduced by a factor of 4 when compared to the pristine material and a dipole moment along the out-of-plane axis due to the defect-induced symmetry breaking. Altogether, these results suggest that the vacancy significantly modifies the excitonic properties of the system, demonstrating the importance of considering defects in the context of material design.
Research Organization:
Boston Univ., MA (United States)
Sponsoring Organization:
National Science Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC02-05CH11231; SC0018080
OSTI ID:
1641730
Journal Information:
Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 7 Vol. 4; ISSN PRMHAR; ISSN 2475-9953
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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2-dimensional systems
36 MATERIALS SCIENCE
Bethe-Salpeter equation
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semiconductors