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Two-dimensional gallium nitride realized via graphene encapsulation

Abstract

The spectrum of two-dimensional (2D) and layered materials ‘beyond graphene’ offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (5.0–6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices1. A gap, however, remains between the theoretical prediction of 2D nitrides ‘beyond hBN’2,3 and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory2,3,4. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.

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Figure 1: Properties of 2D nitrides from ab initio hybrid density functional theory.
Figure 2: 2D GaN formation via migration-enhanced encapsulated growth (MEEG).
Figure 3: Pathways for intercalation and structure of 2D GaN.
Figure 4: Role of graphene in the atomic stabilization of 2D nitrides.
Figure 5: Density of state (DOS) calculations, bandgap (Eg) and electrical measurements of 2D GaN.

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Acknowledgements

Materials and experimental methods in this work were partially supported by Asahi Glass Japan and the National Science Foundation under grant numbers DMR-1006763 (J.M.R.), DMR-1410765 (J.M.R.), DMR-1420620 (J.M.R & J.A.R Seed Program through Penn State MRSEC—Center for Nanoscale Science) and DMR-1453924 (J.A.R.). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Material characterization described in this work was supported by The Pennsylvania State University (PSU) Materials Characterization Laboratory (MCL) Staff Innovation Funding (SIF) Program, and the Alfred P. Sloan Foundation, USA. Theoretical work (S.D.) and XPS analysis (R.M.W.) was supported by the Center for Low Energy Systems Technology (LEAST). LEAST is one of six Semiconductor Research Corporation STARnet centres sponsored by MARCO and DARPA. We would like acknowledge V. Bojan (staff scientist, MCL) and J. Maier (technical staff, MCL) for contributions in AES analysis and FIB-TEM specimen preparation, respectively. In addition, we also acknowledge the microscopy and spectroscopy assistance provided by: N. Alem (PSU); K. Bernd (PSU); A. Azizi (PSU); J. Tischler (NRL); C. Ellis (NRL); J. Owrutsky (NRL) and T. Miyagi (Asahi Glass, Japan). Finally, we thank T. Tiwald (J.A. Woolam) for his assistance in developing the ellipsometric model with J.D.C. and P. Sheehan (NRL) for his beneficence in allowing us to use his ellipsometer.

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Contributions

Experiments were designed by Z.Y.A., J.M.R. and J.A.R. The MEEG process development, SEM, Raman and data analysis (electrical, microscopic and spectroscopic) were performed by Z.Y.A. High-resolution electron microscopy was conducted by K.W. and ABF-STEM simulations by G.S. Moreover, R.K.G. and S.D. designed and implemented theoretical calculations and structure simulations. R.A.V., S.M.E. and S.S. carried out epitaxial graphene growth and quality assessment. UV-Vis measurements were performed at NRL by P.A.D. and J.D.C.; J.D.C. also performed ellipsometric measurements and model development. X.Q. and R.M.W. performed the plasma processing, XPS measurements and analysis at UT Dallas. Y.-C.L. performed vertical transport measurements using C-AFM and S.D. provided input on IV characteristics. Finally, D.F.P. performed AES measurements at PHI. All authors discussed results at all stages. Z.Y.A., J.A.R. and J.M.R. wrote the paper.

Corresponding authors

Correspondence to Joan M. Redwing or Joshua A. Robinson.

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The authors declare no competing financial interests.

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Al Balushi, Z., Wang, K., Ghosh, R. et al. Two-dimensional gallium nitride realized via graphene encapsulation. Nature Mater 15, 1166–1171 (2016). https://doi.org/10.1038/nmat4742

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