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A 7-eV bandgap semiconductor based on silicon-doped α-(Al<sub><i>x</i></sub>Ga<sub>1−<i>x</i></sub>)<sub>2</sub>O<sub>3</sub>

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Data availability

The data supporting the results of this study are available in the paper, its Extended Data figures and the Supplementary Information. The raw data used to create figures are available upon request to the corresponding author.

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Acknowledgements

We thank C. Chang for assistance with wire bonding sample A27.

Funding

J.S., D.B., K.N., N.A.P., M.R., D.A.M., H.G.X., D.J. and D.G.S. acknowledge support from the AFOSR/AFRL ACCESS Center of Excellence under award number FA9550-18-1-0529. This work used the Cornell Center for Materials Research Shared Facilities. Device processing was performed with the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the NSF (Grant NNCI 2025233). This work also made use of the Cornell Energy Systems Institute Shared Facilities partly sponsored by the NSF (Grant MRI DMR 1631282). J.S. acknowledges support from the National Science Foundation (Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM)), under Cooperative Agreement number DMR-2039380. The Thermo Fisher Spectra 300 X-CFEG was acquired with support from PARADIM, an NSF MIP (DMR-2039380), and Cornell University. N.A.P. acknowledges support from National Science Foundation Graduate Research Fellowship under grant number DGE2139899. S.D. and B.M. acknowledge support from National Science Foundation (NSF) under the Division of Materials Research (DMR) through grant number 2145091. I.S. and B.M. acknowledge the support from internal seed UB launch funding from the University at Buffalo and instrument support (FIB–SEM) from the Northeast Regional Defense Technology Hub. M.S. acknowledges support by NSF (grants ECCS 2329940 and OIA-2044049 Emergent Quantum Materials and Technologies), by AFOSR (grants FA9550-23-1-0574 DEF and FA9550-25-1-0196), and by the J.A. Woollam Foundation. M.K.I.S. and M.D.W. acknowledge support from the Department of Education, 84.031B Historically Black Colleges and Universities Program - P031B170007–20, and together with D.G.S., acknowledge grant PREM-DMR-2122147 with the National Science Foundation. V.-A.H., N.P. and F.G. were supported by SUPREME, one of seven centres in JUMP 2.0, a Semiconductor Research Corporation (SRC) programme sponsored by DARPA (mobility calculations), and by the Computational Materials Sciences Program funded by the US Department of Energy, Office of Science, Basic Energy Sciences, under award number DE-SC0020129 (development of the EPW code). This work used stampede3 at TACC through allocation PHY260047 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) programme, which is supported by US National Science Foundation grant numbers 2138259, 2138286, 2138307, 2137603 and 2138296.

Author information

Author notes

  1. These authors contributed equally: Jacob Steele, Debaditya Bhattacharya

Authors and Affiliations

  1. Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA

    Jacob Steele, Naomi A. Pieczulewski, Huili G. Xing, Debdeep Jena & Darrell. G. Schlom

  2. School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA

    Debaditya Bhattacharya, Kazuki Nomoto, Madhav Ramesh, Huili G. Xing & Debdeep Jena

  3. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, USA

    Preston Sorensen, Ufuk Kilic & Mathias Schubert

  4. Oden Institute for Computational Engineering and Sciences, University of Texas at Austin, Austin, TX, USA

    Viet-Anh Ha, Nick Pant & Feliciano Giustino

  5. Department of Physics, University of Texas Austin, Austin, TX, USA

    Viet-Anh Ha, Nick Pant & Feliciano Giustino

  6. Department of Materials Design and Innovation, University at Buffalo, Buffalo, NY, USA

    Ihit Shukla, Shaon Das & Baishakhi Mazumder

  7. Department of Physics, Clark Atlanta University, Atlanta, GA, USA

    M. K. Indika Senevirathna & Michael D. Williams

  8. Department of Physics, Solid State Physics, Wallenberg Initiative Materials Science for Sustainability (WISE), Lund, Sweden

    Mathias Schubert

  9. Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA

    David A. Muller, Huili G. Xing, Debdeep Jena & Darrell. G. Schlom

  10. School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA

    David A. Muller

  11. Leibniz-Institut für Kristallzüchtung, Berlin, Germany

    Darrell. G. Schlom

Authors

  1. Jacob Steele
  2. Debaditya Bhattacharya
  3. Kazuki Nomoto
  4. Naomi A. Pieczulewski
  5. Preston Sorensen
  6. Viet-Anh Ha
  7. Nick Pant
  8. Ihit Shukla
  9. Shaon Das
  10. Ufuk Kilic
  11. Madhav Ramesh
  12. Feliciano Giustino
  13. Baishakhi Mazumder
  14. M. K. Indika Senevirathna
  15. Michael D. Williams
  16. Mathias Schubert
  17. David A. Muller
  18. Huili G. Xing
  19. Debdeep Jena
  20. Darrell. G. Schlom

Contributions

J.S. conceived of the original experiment, carried out all MBE growth, and conducted all the XRD, atomic force microscopy and Hall measurements. D.B. managed mask design, patterning of devices onto the thin films and measurement of device behaviour. J.S. and D.B. jointly wrote the article text and conducted physical property measurement system measurements. K.N. created recipes for ohmic and Schottky contacts. N.A.P. conducted all STEM imaging. P.S. handled the ellipsometry measurements with assistance from U.K. M.R. assisted D.B. with measuring the breakdown voltage of the AlphaDiodes. M.K.I.S. and M.D.W. carried out the SIMS measurements. V.-A.H., N.P. and F.G. calculated the theoretical mobilities as a function of x using density functional theory (Fig. 2e). I.S. performed focused-ion-beam specimen preparation and APT measurements. S.D. performed APT measurements and data analysis. B.M. supervised the APT experiments and data analysis. M.S. oversaw the ellipsometry measurements. D.A.M. oversaw the STEM measurements. H.G.X. and D.J. helped design the devices, assisted in analysing the results and edited the paper. D.G.S. oversaw the MBE growths, helped conceive of the experiments, assisted in the analysis of the results and was the primary editor of the article drafts.

Corresponding author

Correspondence to Darrell. G. Schlom.

Ethics declarations

Competing interests

D.G.S. has been granted US patent number 11,462,402 (4 October 2022) with the title ‘Suboxide molecular-beam epitaxy and related structures’. J.S., D.B., H.G.X., D.J. and D.G.S. have filed a provisional US patent 63/786,244 with the title ‘A procedure for growing conductive silicon-doped α-(Al,Ga)2O3 by suboxide molecular-beam epitaxy’. The patent covers the epitaxial structure described in this article that enables conductive α-(AlxGa1−x)2O3 films, as well as multiple device structures utilizing α-(AlxGa1−x)2O3 channels.

Peer review

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Nature thanks Hironori Okumura and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 High-resolution transmission electron microscopy of interfaces in an AlphaFET on sample A1.

a, A cross section of the entire AlphaFET structure with all epitaxial layers labeled. b, The interface between the m-plane sapphire substrate and the initial high Tsub α-(Al0.58Ga0.42)2O3 buffer layer. Misfit dislocations are observed at the interface and are marked by the white “⊤” symbols. The interfaces are atomically sharp and flat. c, An image of the interface between the first high Tsub α-(Al0.58Ga0.42)2O3 buffer layer and the subsequent Tsub α-(Al0.51Ga0.49)2O3 buffer layer grown at moderate Tsub. d, An image of the interface between the silicon-doped α-(Al0.51Ga0.49)2O3 channel layer grown at low Tsub and the n+ regrown α-(Al0.25Ga0.75)2O3 contact layer. e, The last epitaxial interface between the regrown n+ regrown α-(Al0.25Ga0.75)2O3 and α-Ga2O3 contact layers. Misfit dislocations are also seen at this interface, and one is marked by the white “⊤” symbol.

Extended Data Fig. 2 AFM scan of sample A26.

An AFM image of a 5 µm × 5 µm region on the surface of sample A26 as a representative as-grown surface of AlphaFET structures The color gradient is linear with the size of the features on the surface.

Extended Data Fig. 3 Raw ellipsometry data.

A plot of the M12 and M33 Mueller matrix elements for sample A1 and the corresponding fit to a 4-layer model which includes the substrate, the initial high Tsub α-(Al0.58Ga0.42)2O3 buffer layer, the subsequent moderate Tsub α-(Al0.51Ga0.49)2O3 buffer layer, and the overlying silicon-doped α-(Al0.51Ga0.49)2O3 channel layer. Due to anisotropy in the crystal, the data were collected for 3 azimuthal angles 0°, 45°, and 90° to the [0001] direction. The green, red, and blue points represent data taken at 50°, 60°, and 70° angles of incidence (AOI). The dashed lines mark the fits of the data that was used to estimate Eg.

Extended Data Fig. 4 Temperature-dependent sheet resistivity and Hall measurements on sample A27.

a, A plot of Rs as a function of T. Approximately a 10× increase in Rs as sample is cooled from 300 K to 200 K. The fit is performed by assuming a constant mobility of \(\mu \) = 2 cm2/V·s which is then used to estimate the carrier density. This carrier density is then used to fit the donor density ND and donor activation energy ED. b, A plot of the electron concentration ne as extracted from temperature-dependent Hall measurements as a function of T. The carrier concentration drops with decreasing temperature indicating the start of freezing out of carriers. In a similar fashion to panel a, the carrier concentration is fit to find ND and ED.

Extended Data Fig. 5 Measurements on A27 to determine the efficacy of regrowth for ohmic contacts.

a, TLM measurements of the contacts as measured through the regrown layer. Inset is the I-V curves for each contact spacing that yields the resistance as a function of spacing in the primary plot. b, An I-V plot of measurements taken through the channel without regrowth.

Extended Data Fig. 6 θ−2θ scans of samples A8 and A10 over the range of 2θ = (50–70)°.

The ‘*’ symbol marks the 300 reflection of the Al2O3 substrate. Both A8 and A10 show sharp 300 α-(AlxGa1−x)2O3 reflections that correspond to the doped overlayers with x = 0.52 and 0.54, respectively.

Extended Data Fig. 7 θ−2θ scans of samples A8 and A9 over the range of 2θ = (64–70)°.

The ‘*’ symbol marks the 300 reflection of the Al2O3 substrate. The intense 300 reflection for α-(Al0.52Ga0.48)2O3 corresponds to the overlayer of sample A8. The low intensity hump on the right edge of the 300 reflection in sample A8 is the buffer layer that was deposited at high Tsub prior to the overlayer. In sample A9, only a broad, weak reflection is seen, which is consistent with limited crystalline, epitaxial α-(AlxGa1−x)2O3 successfully being grown.

Extended Data Fig. 8 Results of SIMS and APT measurements on sample A1.

Depth profile of a, aluminium ion intensity b, gallium ion intensity c, silicon concentration by SIMS. The solid line shows the as-measured silicon concentration. The horizontal dashed line represents the estimated 1.18 × 1019 cm−3 noise-floor for silicon concentrations in the SIMS set-up. d, The spatial distribution of silicon (grey), aluminium (red), and gallium (blue) in the needle-shaped tip used for APT. e, The distribution of aluminium and gallium atoms in the green region of panel d compared to a binomial spread. f, The distribution of aluminium and gallium atoms in the blue region of panel d compared to a binomial spread.

Extended Data Fig. 9 The theoretical scattering mechanism and directional dependent maximum values of µe for α-(AlxGa1–x)2O3 as a function of x with varying ne.

a, ne = 1016 cm−3. b, ne = 1017 cm−3. c, ne = 1018 cm−3. d, ne = 1019 cm−3, where the ionized impurity density is assumed to be equal to ne. The theoretical maximum values of µe are calculated including contributions from phonon scattering (ph), ionized impurity scattering (ii), and alloy scattering. The solid ∥ line is for electron transport parallel to the (001) plane, and the dashed ⊥ line is perpendicular to the (001) plane.

Extended Data Table 1 The compositions, thicknesses, estimated channel Eg, and the room-temperature electronic properties measured by the Hall effect of the channel including ne, µe, Rs and σ of each film in this study

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Steele, J., Bhattacharya, D., Nomoto, K. et al. A 7-eV bandgap semiconductor based on silicon-doped α-(AlxGa1−x)2O3. Nature (2026). https://doi.org/10.1038/s41586-026-11085-3

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  • DOI: https://doi.org/10.1038/s41586-026-11085-3