Remote epitaxy through graphene enables two-dimensional material-based layer transfer

Journal name:
Nature
Volume:
544,
Pages:
340–343
Date published:
DOI:
doi:10.1038/nature22053
Received
Accepted
Published online

Epitaxy—the growth of a crystalline material on a substrate—is crucial for the semiconductor industry, but is often limited by the need for lattice matching between the two material systems. This strict requirement is relaxed for van der Waals epitaxy1, 2, 3, 4, 5, 6, 7, 8, 9, 10, in which epitaxy on layered or two-dimensional (2D) materials is mediated by weak van der Waals interactions, and which also allows facile layer release from 2D surfaces3, 8. It has been thought that 2D materials are the only seed layers for van der Waals epitaxy3, 4, 5, 6, 7, 8, 9, 10. However, the substrates below 2D materials may still interact with the layers grown during epitaxy (epilayers), as in the case of the so-called wetting transparency documented for graphene11, 12, 13. Here we show that the weak van der Waals potential of graphene cannot completely screen the stronger potential field of many substrates, which enables epitaxial growth to occur despite its presence. We use density functional theory calculations to establish that adatoms will experience remote epitaxial registry with a substrate through a substrate–epilayer gap of up to nine ångströms; this gap can accommodate a monolayer of graphene. We confirm the predictions with homoepitaxial growth of GaAs(001) on GaAs(001) substrates through monolayer graphene, and show that the approach is also applicable to InP and GaP. The grown single-crystalline films are rapidly released from the graphene-coated substrate and perform as well as conventionally prepared films when incorporated in light-emitting devices. This technique enables any type of semiconductor film to be copied from underlying substrates through 2D materials, and then the resultant epilayer to be rapidly released and transferred to a substrate of interest. This process is particularly attractive in the context of non-silicon electronics and photonics, where the ability to re-use the graphene-coated substrates8 allows savings on the high cost of non-silicon substrates.

At a glance

Figures

  1. Substrate–epilayer remote interaction with different gaps created by different numbers of stacked graphene interlayers.
    Figure 1: Substrate–epilayer remote interaction with different gaps created by different numbers of stacked graphene interlayers.

    a, b, Main plots, results of DFT calculations of averaged electron density along separated slabs of GaAs for As–Ga interaction (a) and As–As interaction (b). Periodic boundary conditions were imposed along the dashed lines of the simulation model (shown at top). Both plots show the existence of significant electron charge density between the separated slabs within a gap of about 9 Å. ce, EBSD maps of GaAs grown on and exfoliated from ‘monolayer’ graphene–GaAs(001) substrate (c), showing (001) single-crystallinity, and of GaAs grown on and exfoliated from ‘bilayer’ (d) and ‘tetralayer’ (e) graphene–GaAs(001) substrate showing (111)-dominant polycrystallinity. On the left is the inverse pole figure colour triangle for crystallographic orientations.

  2. Characterization of GaAs grown on the monolayer graphene–GaAs(001) substrate.
    Figure 2: Characterization of GaAs grown on the monolayer graphene–GaAs(001) substrate.

    a, Large-scale EBSD map of exfoliated GaAs. b, High-resolution X-ray diffraction azimuthal off-axis ϕ scan of the same exfoliated GaAs layer, representing a single-crystalline zinc-blende structure without in-plane rotations. c, EBSD map of an exfoliated GaAs layer grown on a monolayer graphene–GaAs substrate without H2 annealing after transfer. d, High-resolution STEM images showing excellent remote alignment of the GaAs(001) lattices through the graphene. Convergent-beam electron diffraction patterns from the epilayer (top inset) and the substrate (bottom inset) show identical zinc-blende (001) orientations. e, Low-angle annular dark field STEM image showing no dislocations.

  3. AlGaInP–GaInP double heterojunction LEDs on a graphene–GaAs substrate.
    Figure 3: AlGaInP–GaInP double heterojunction LEDs on a graphene–GaAs substrate.

    a, Cross-sectional SEM image of heterojunction LEDs. b, IV curves of LEDs grown on graphene–GaAs substrates and directly on GaAs. Inset, emitted red light from the LEDs grown on the graphene–GaAs substrate. c, Electroluminescence spectra of the LEDs grown on graphene–GaAs substrates and directly on GaAs, Inset, photographs of functioning LEDs grown on both substrates.

  4. Single-crystalline III-V(001) films exfoliated from graphene–III-V(001) substrates after remote epitaxy.
    Figure 4: Single-crystalline III-V(001) films exfoliated from graphene–III-V(001) substrates after remote epitaxy.

    a, d, g, GaAs; b, e, h, InP; c, f, i, GaP. Schematic illustration (top left) shows the exfoliation process of thin-film sample preparation for high-resolution X-ray diffraction and EBSD characterizations. ac, Photographs of single-crystalline GaAs(001), InP(001), and GaP(001) films exfoliated from graphene–III-V(001) substrates. df, High-resolution X-ray diffraction ω–2θ scans of the exfoliated semiconductor/stressor stack that includes GaAs(001), InP(001), and GaP(001) epilayers. gi, Large-scale EBSD maps of GaAs(001), InP(001), and GaP(001) epilayer surfaces.

  5. Natural slab separation with n graphene layers present between GaAs slabs.
    Extended Data Fig. 1: Natural slab separation with n graphene layers present between GaAs slabs.

    To determine the maximum number of graphene layers that can be inserted within this critical gap, we calculate the natural separation induced by graphene interlayers using the structure shown on the left. The results show that the graphene–As distance d3 is 3.14 Å, the graphene–graphene distance d2 is 3.15 Å and the graphene–Ga distance d1 is 1.9 Å. A detailed description of calculated distances is in the table at the bottom for both Ga–As and As–As terminated cases.

  6. SEM images of front grown surface and released surface of GaAs films grown on monolayer, bilayer and tetralayer graphene stacks transferred onto GaAs(001) substrates.
    Extended Data Fig. 2: SEM images of front grown surface and released surface of GaAs films grown on monolayer, bilayer and tetralayer graphene stacks transferred onto GaAs(001) substrates.

    a, The front surface of the GaAs epilayer grown on monolayer graphene–GaAs substrate is generally smooth but also contains impinging marks which need to be addressed by further optimization of nucleation and growth. Inset, 1 μm × 1 μm non-contact AFM scan; the epitaxial layer appears to be growing via step flow growth. The r.m.s. roughness of the AFM scan is 0.3 nm. b, c, Three-dimensional growth was observed for films grown on thicker graphene–substrates owing to limited registry from the substrates. Scale bars, 4 μm. Top and bottom panels of ac indicate front and released surfaces, respectively.

  7. HRXRD ω–2θ scans of ‘exfoliated’ GaAs epilayers.
    Extended Data Fig. 3: HRXRD ω–2θ scans of ‘exfoliated’ GaAs epilayers.

    a, Diagram of exfoliated stacks of GaAs released from a graphene–GaAs(001) substrate. b, ω–2θ scan of GaAs exfoliated from monolayer graphene transferred on a GaAs(001) substrate showing (001) single-crystallinity as indicated by XRD peaks of the (002) and (004) lattice labelled in red. c, ω–2θ scan of GaAs exfoliated from bilayer graphene transferred on GaAs(100) substrate showing polycrystallinity with dominant (111) orientation, as indicated by the XRD peak of the (111) lattice labelled in red, and d, ω–2θ scan of GaAs exfoliated from tetralayer graphene transferred on a GaAs(001) substrate showing polycrystallinity with dominant (111) orientation, also indicated by XRD peak of the (111) lattice labelled in red. The ω–2θ scans also picked up XRD peaks from the Ni stressor film and the Ti adhesion layer that was used to exfoliate the GaAs films (Methods). The presence of these films are shown by the XRD peak of the (111) Ni lattice and the (101) lattice of anatase TiO2 from the Ti layer.

  8. GaAs(111) films grown on a monolayer graphene–GaAs(111)B substrate.
    Extended Data Fig. 6: GaAs(111) films grown on a monolayer graphene–GaAs(111)B substrate.

    Schematic illustration at left shows exfoliation process of a thin-film GaAs(111) epilayer. The EBSD map demonstrates the versatility of the method used to copy the substrate orientation through graphene by remote homoepitaxy. On the right is the inverse pole figure colour triangle for crystallographic orientations. a, EBSD map of the released surface of a GaAs(111) layer substrate. b, SEM image of the front surface, as grown. c, SEM image of the released surface.

  9. Steady-state room temperature photoluminescence spectra.
    Extended Data Fig. 4: Steady-state room temperature photoluminescence spectra.

    Shown are steady-state photoluminescence spectra of GaAs substrate and exfoliated GaAs epilayer grown by remote epitaxy.

  10. LED light emission before and after transfer.
    Extended Data Fig. 5: LED light emission before and after transfer.

    a, Diagram of the graphene-based layer transfer of LEDs. b, I–V curves of LEDs before and after transfer. c, Light emission of LEDs before and after transfer.

  11. Plan-view SEM of exfoliated surface of GaAs.
    Extended Data Fig. 7: Plan-view SEM of exfoliated surface of GaAs.

    a, Smooth parts indicate release from graphene, and rough parts indicate spalling directly from GaAs substrate surface through graphene defects. If mechanical defects such as holes and cracks in graphene exist, they permit direct exposure of the GaAs(001) surface to adatoms, resulting in the direct binding of adatoms to the substrate. Location of b is shown boxed. b, Direct epitaxy of GaAs epilayers on GaAs substrates causes jagged topology (spalling marks) upon exfoliation due to the occurrence of spalling. However, such marks are observed in limited areas.

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Author information

  1. These authors contributed equally to this work.

    • Yunjo Kim,
    • Samuel S. Cruz &
    • Kyusang Lee

Affiliations

  1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Yunjo Kim,
    • Samuel S. Cruz,
    • Kyusang Lee,
    • Babatunde O. Alawode,
    • Chanyeol Choi,
    • Wei Kong,
    • Shinhyun Choi,
    • Kuan Qiao,
    • Ibraheem Almansouri,
    • Alexie M. Kolpak &
    • Jeehwan Kim
  2. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Yi Song &
    • Jing Kong
  3. Department of Materials Science and Engineering, Ohio State University, Columbus, Ohio 43210, USA

    • Jared M. Johnson &
    • Jinwoo Hwang
  4. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Christopher Heidelberger,
    • Eugene A. Fitzgerald &
    • Jeehwan Kim
  5. Department of Electrical Engineering and Computer Science, Masdar Institute of Science and Technology, Abu Dhabi 54224, United Arab Emirates

    • Ibraheem Almansouri
  6. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Jing Kong &
    • Jeehwan Kim

Contributions

J. Kim conceived the 2DLT process, designed experiments, and directed the team. Y.K., S.S.C., K.L., C.C., Y.S., C.H., W.K., S.C., K.Q. and I.A. performed the epitaxial growths/transfer experiments and characterization. K.L. fabricated and measured LED devices. J.M.J. and J.H. performed TEM analysis. B.O.A. contributed to the computational model and DFT simulation. All authors contributed to the discussion and analysis of the results regarding the manuscript.

Competing financial interests

The authors declare no competing financial interests.

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Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: Natural slab separation with n graphene layers present between GaAs slabs. (167 KB)

    To determine the maximum number of graphene layers that can be inserted within this critical gap, we calculate the natural separation induced by graphene interlayers using the structure shown on the left. The results show that the graphene–As distance d3 is 3.14 Å, the graphene–graphene distance d2 is 3.15 Å and the graphene–Ga distance d1 is 1.9 Å. A detailed description of calculated distances is in the table at the bottom for both Ga–As and As–As terminated cases.

  2. Extended Data Figure 2: SEM images of front grown surface and released surface of GaAs films grown on monolayer, bilayer and tetralayer graphene stacks transferred onto GaAs(001) substrates. (287 KB)

    a, The front surface of the GaAs epilayer grown on monolayer graphene–GaAs substrate is generally smooth but also contains impinging marks which need to be addressed by further optimization of nucleation and growth. Inset, 1 μm × 1 μm non-contact AFM scan; the epitaxial layer appears to be growing via step flow growth. The r.m.s. roughness of the AFM scan is 0.3 nm. b, c, Three-dimensional growth was observed for films grown on thicker graphene–substrates owing to limited registry from the substrates. Scale bars, 4 μm. Top and bottom panels of ac indicate front and released surfaces, respectively.

  3. Extended Data Figure 3: HRXRD ω–2θ scans of ‘exfoliated’ GaAs epilayers. (271 KB)

    a, Diagram of exfoliated stacks of GaAs released from a graphene–GaAs(001) substrate. b, ω–2θ scan of GaAs exfoliated from monolayer graphene transferred on a GaAs(001) substrate showing (001) single-crystallinity as indicated by XRD peaks of the (002) and (004) lattice labelled in red. c, ω–2θ scan of GaAs exfoliated from bilayer graphene transferred on GaAs(100) substrate showing polycrystallinity with dominant (111) orientation, as indicated by the XRD peak of the (111) lattice labelled in red, and d, ω–2θ scan of GaAs exfoliated from tetralayer graphene transferred on a GaAs(001) substrate showing polycrystallinity with dominant (111) orientation, also indicated by XRD peak of the (111) lattice labelled in red. The ω–2θ scans also picked up XRD peaks from the Ni stressor film and the Ti adhesion layer that was used to exfoliate the GaAs films (Methods). The presence of these films are shown by the XRD peak of the (111) Ni lattice and the (101) lattice of anatase TiO2 from the Ti layer.

  4. Extended Data Figure 4: GaAs(111) films grown on a monolayer graphene–GaAs(111)B substrate. (275 KB)

    Schematic illustration at left shows exfoliation process of a thin-film GaAs(111) epilayer. The EBSD map demonstrates the versatility of the method used to copy the substrate orientation through graphene by remote homoepitaxy. On the right is the inverse pole figure colour triangle for crystallographic orientations. a, EBSD map of the released surface of a GaAs(111) layer substrate. b, SEM image of the front surface, as grown. c, SEM image of the released surface.

  5. Extended Data Figure 5: Steady-state room temperature photoluminescence spectra. (87 KB)

    Shown are steady-state photoluminescence spectra of GaAs substrate and exfoliated GaAs epilayer grown by remote epitaxy.

  6. Extended Data Figure 6: LED light emission before and after transfer. (152 KB)

    a, Diagram of the graphene-based layer transfer of LEDs. b, I–V curves of LEDs before and after transfer. c, Light emission of LEDs before and after transfer.

  7. Extended Data Figure 7: Plan-view SEM of exfoliated surface of GaAs. (109 KB)

    a, Smooth parts indicate release from graphene, and rough parts indicate spalling directly from GaAs substrate surface through graphene defects. If mechanical defects such as holes and cracks in graphene exist, they permit direct exposure of the GaAs(001) surface to adatoms, resulting in the direct binding of adatoms to the substrate. Location of b is shown boxed. b, Direct epitaxy of GaAs epilayers on GaAs substrates causes jagged topology (spalling marks) upon exfoliation due to the occurrence of spalling. However, such marks are observed in limited areas.

Additional data