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Real-space observation of a two-dimensional electron gas at semiconductor heterointerfaces

Nature Nanotechnology volume 18, pages 521–528 (2023)Cite this article

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Abstract

Mobile charge carriers are essential components in high-performance, nano-engineered semiconductor devices. Employing charge carriers confined to heterointerfaces, the so-called two-dimensional electron gas, is essential for improving device performance. The real-space visualization of a two-dimensional electron gas at the nanometre scale is desirable. However, it is challenging to accomplish by means of electron microscopy due to an unavoidable strong diffraction contrast formation at the heterointerfaces. We performed direct, nanoscale electric field imaging across a GaN-based semiconductor heterointerface using differential phase contrast scanning transmission electron microscopy by suppressing diffraction contrasts. For both nearly the lattice-matched GaN/Al0.81In0.19N interface and pseudomorphic GaN/Al0.88In0.12N interface, the extracted quantitative electric field profiles show excellent agreement with profiles predicted using Poisson simulation. Furthermore, we used the electric field profiles to quantify the density and distribution of the two-dimensional electron gas across the heterointerfaces with nanometre precision. This study is expected to guide the real-space characterization of local charge carrier density and distribution in semiconductor devices.

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Fig. 1: Schematic diagrams of the DPC STEM and tDPC STEM techniques.
Fig. 2: GaN/AlInN samples.
Fig. 3: The tDPC STEM results.
Fig. 4: Comparison between experimental tDPC images and the Poisson simulation.

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Data availability

The data supporting the findings of this study are available within the paper. The DPC, HAADF and EDS images are available on the GitHub repository (https://github.com/sigma-users/GaNAlInNdata).

References

  1. Ambacher, O. et al. Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures. J. Appl. Phys. 87, 334–344 (2000).

    Article  CAS  Google Scholar 

  2. Ambacher, O. et al. Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures. J. Appl. Phys. 85, 3222–3233 (1999).

    Article  CAS  Google Scholar 

  3. Ohta, H. et al. Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3. Nat. Mater. 6, 129–134 (2007).

    Article  CAS  Google Scholar 

  4. Ferain, I., Colinge, C. A. & Colinge, J.-P. Multigate transistors as the future of classical metal–oxide–semiconductor field-effect transistors. Nature 479, 310–316 (2011).

    Article  CAS  Google Scholar 

  5. Syaranamual, G. J. et al. Role of two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistor (HEMT) ON-state degradation. Microelectron. Reliab. 64, 589–593 (2016).

    Article  CAS  Google Scholar 

  6. Kaushik, P. K., Singh, S. K., Gupta, A., Basu, A. & Chang, E. Y. Impact of surface states and aluminum mole fraction on surface potential and 2DEG in AlGaN/GaN HEMTs. Nanoscale Res. Lett. 16, 159 (2021).

    Article  CAS  Google Scholar 

  7. Smorchkova, I. P. et al. Polarization-induced charge and electron mobility in AlGaN/GaN heterostructures grown by plasma-assisted molecular-beam epitaxy. J. Appl. Phys. 86, 4520–4526 (1999).

    Article  CAS  Google Scholar 

  8. Ibbetson, J. P. et al. Polarization effects, surface states, and the source of electrons in AlGaN/GaN heterostructure field effect transistors. Appl. Phys. Lett. 77, 250–252 (2000).

    Article  CAS  Google Scholar 

  9. Zheng, Z. et al. Gallium nitride-based complementary logic integrated circuits. Nat. Electron. 4, 595–603 (2021).

    Article  CAS  Google Scholar 

  10. Joh, J. & del Alamo, J. A. A current-transient methodology for trap analysis for GaN high electron mobility transistors. IEEE Trans. Electron Devices 58, 132–140 (2011).

    Article  CAS  Google Scholar 

  11. Pearton, S. J., Ren, F., Patrick, E., Law, M. E. & Polyakov, A. Y. Review—ionizing radiation damage effects on GaN devices. ECS J. Solid State Sci. Technol. 5, Q35–Q60 (2016).

    Article  CAS  Google Scholar 

  12. Nakagami, K., Ohno, Y., Kishimoto, S., Maezawa, K. & Mizutani, T. Surface potential measurements of AlGaN/GaN high-electron-mobility transistors by Kelvin probe force microscopy. Appl. Phys. Lett. 85, 6028–6029 (2004).

    Article  CAS  Google Scholar 

  13. Masuda, H., Ishida, N., Ogata, Y., Ito, D. & Fujita, D. Internal potential mapping of charged solid-state-lithium ion batteries using in situ Kelvin probe force microscopy. Nanoscale 9, 893–898 (2017).

    Article  CAS  Google Scholar 

  14. Cao, Y., Pomeroy, J. W., Uren, M. J., Yang, F. & Kuball, M. Electric field mapping of wide-bandgap semiconductor devices at a submicrometre resolution. Nat. Electron. 4, 478–485 (2021).

    Article  CAS  Google Scholar 

  15. Shibata, N. et al. Differential phase-contrast microscopy at atomic resolution. Nat. Phys. 8, 611–615 (2012).

    Article  CAS  Google Scholar 

  16. Müller-Caspary, K. et al. Electrical polarization in AlN/GaN nanodisks measured by momentum-resolved 4D scanning transmission electron microscopy. Phys. Rev. Lett. 122, 106102 (2019).

    Article  Google Scholar 

  17. Song, K. et al. Direct imaging of the electron liquid at oxide interfaces. Nat. Nanotechnol. 13, 198–203 (2018).

    Article  CAS  Google Scholar 

  18. Wolf, D. et al. Unveiling the three-dimensional magnetic texture of skyrmion tubes. Nat. Nanotechnol. 17, 250–255 (2022).

    Article  CAS  Google Scholar 

  19. Mawson, T. et al. Suppressing dynamical diffraction artefacts in differential phase contrast scanning transmission electron microscopy of long-range electromagnetic fields via precession. Ultramicroscopy 219, 113097 (2020).

    Article  CAS  Google Scholar 

  20. Haas, B., Rouvière, J.-L., Boureau, V., Berthier, R. & Cooper, D. Direct comparison of off-axis holography and differential phase contrast for the mapping of electric fields in semiconductors by transmission electron microscopy. Ultramicroscopy 198, 58–72 (2019).

    Article  CAS  Google Scholar 

  21. Yamamoto, K., Anada, S., Sato, T., Yoshimoto, N. & Hirayama, T. Phase-shifting electron holography for accurate measurement of potential distributions in organic and inorganic semiconductors. Microscopy 70, 24–38 (2021).

    Article  CAS  Google Scholar 

  22. Marino, F. A., Cullen, D. A., Smith, D. J., McCartney, M. R. & Saraniti, M. Simulation of polarization charge on AlGaN/GaN high electron mobility transistors: comparison to electron holography. J. Appl. Phys. 107, 054516 (2010).

    Article  Google Scholar 

  23. Wu, Z. H. et al. Mapping the electrostatic potential across AlGaN/AlN/GaN heterostructures using electron holography. Appl. Phys. Lett. 90, 032101 (2007).

    Article  Google Scholar 

  24. Kohno, Y., Nakamura, A., Morishita, S. & Shibata, N. Development of tilt-scan system for differential phase contrast scanning transmission electron microscopy. Microscopy 71, 111–116 (2022).

    Article  Google Scholar 

  25. Toyama, S. et al. Quantitative electric field mapping in semiconductor heterostructures via tilt-scan averaged DPC STEM. Ultramicroscopy 238, 113538 (2022).

    Article  CAS  Google Scholar 

  26. Lippmann, B. A. Ehrenfest’s theorem and scattering theory. Phys. Rev. Lett. 15, 11–14 (1965).

    Article  Google Scholar 

  27. Close, R., Chen, Z., Shibata, N. & Findlay, S. D. Towards quantitative, atomic-resolution reconstruction of the electrostatic potential via differential phase contrast using electrons. Ultramicroscopy 159, 124–137 (2015).

    Article  CAS  Google Scholar 

  28. Seki, T. et al. Quantitative electric field mapping in thin specimens using a segmented detector: revisiting the transfer function for differential phase contrast. Ultramicroscopy 182, 258–263 (2017).

    Article  CAS  Google Scholar 

  29. Kohno, Y., Seki, T., Findlay, S. D., Ikuhara, Y. & Shibata, N. Real-space visualization of intrinsic magnetic fields of an antiferromagnet. Nature 602, 234–239 (2022).

    Article  CAS  Google Scholar 

  30. Sánchez-Santolino, G. et al. Probing the internal atomic charge density distributions in real space. ACS Nano 12, 8875–8881 (2018).

    Article  Google Scholar 

  31. Ishikawa, R. et al. Direct electric field imaging of graphene defects. Nat. Commun. 9, 3878 (2018).

    Article  Google Scholar 

  32. Gao, W. et al. Real-space charge-density imaging with sub-ångström resolution by four-dimensional electron microscopy. Nature 575, 480–484 (2019).

    Article  CAS  Google Scholar 

  33. Trellakis, A. et al. The 3D nanometer device project nextnano: concepts, methods, results. J. Comput. Electron. 5, 285–289 (2006).

    Article  Google Scholar 

  34. Birner, S. et al. nextnano: general purpose 3-D simulations. IEEE Trans. Electron Devices 54, 2137–2142 (2007).

    Article  CAS  Google Scholar 

  35. Schowalter, M., Rosenauer, A., Lamoen, D., Kruse, P. & Gerthsen, D. Ab initio computation of the mean inner Coulomb potential of wurtzite-type semiconductors and gold. Appl. Phys. Lett. 88, 232108 (2006).

    Article  Google Scholar 

  36. Jain, S. C., Willander, M., Narayan, J. & Overstraeten, R. V. III–Nitrides: growth, characterization, and properties. J. Appl. Phys. 87, 965–1006 (2000).

    Article  CAS  Google Scholar 

  37. Ando, T., Fowler, A. B. & Stern, F. Electronic properties of two-dimensional systems. Rev. Mod. Phys. 54, 437–672 (1982).

    Article  CAS  Google Scholar 

  38. Ando, T. Self-consistent results for a GaAs/AlxGa1–xAs heterojunciton. II. Low temperature mobility. J. Phys. Soc. Jpn 51, 3900–3907 (1982).

    Article  CAS  Google Scholar 

  39. Quang, D. N., Tuoc, V. N., Tung, N. H., Minh, N. V. & Phong, P. N. Roughness-induced mechanisms for electron scattering in wurtzite group-III-nitride heterostructures. Phys. Rev. B 72, 245303 (2005).

    Article  Google Scholar 

  40. Quang, D. N. et al. Quantum and transport lifetimes due to roughness-induced scattering of a two-dimensional electron gas in wurtzite group-III-nitride heterostructures. Phys. Rev. B 74, 205312 (2006).

    Article  Google Scholar 

  41. Kawahara, K. et al. Unique fitting of electrochemical impedance spectra by random walk Metropolis Hastings algorithm. J. Power Sources 403, 184–191 (2018).

    Article  CAS  Google Scholar 

  42. Butté, R. et al. Current status of AlInN layers lattice-matched to GaN for photonics and electronics. J. Phys. D 40, 6328–6344 (2007).

    Article  Google Scholar 

  43. Crespo, A. et al. High-power Ka-band performance of AlInN/GaN HEMT with 9.8-nm-thin barrier. IEEE Electron Device Lett. 31, 2–4 (2010).

    Article  CAS  Google Scholar 

  44. Py, M. A., Lugani, L., Taniyasu, Y., Carlin, J.-F. & Grandjean, N. Shallow donor and deep DX-like center in InAlN layers nearly lattice-matched to GaN. Phys. Rev. B 90, 115208 (2014).

    Article  Google Scholar 

  45. Kappers, M. J., Zhu, T., Sahonta, S. ‐L., Humphreys, C. J. & Oliver, R. A. SCM and SIMS investigations of unintentional doping in III‐nitrides. Phys. Status Solidi C 12, 403–407 (2015).

    Article  CAS  Google Scholar 

  46. Chung, R. B. et al. Growth study and impurity characterization of AlxIn1−xN grown by metal organic chemical vapor deposition. J. Cryst. Growth 324, 163–167 (2011).

    Article  CAS  Google Scholar 

  47. Egerton, R. F. Electron Energy-Loss Spectroscopy in the Electron Microscope (Springer Science & Business Media, 2011).

  48. Shibata, N. et al. Atomic resolution electron microscopy in a magnetic field free environment. Nat. Commun. 10, 2308 (2019).

    Article  CAS  Google Scholar 

  49. Morishita, S. et al. Attainment of 40.5 pm spatial resolution using 300 kV scanning transmission electron microscope equipped with fifth-order aberration corrector. Microscopy 67, 46–50 (2018).

    Article  CAS  Google Scholar 

  50. Tsuda, K. & Tanaka, M. Refinement of crystal structural parameters using two-dimensional energy-filtered CBED patterns. Acta Crystallogr. A 55, 939–954 (1999).

    Article  CAS  Google Scholar 

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Acknowledgements

This work was supported by JST ERATO, grant number JPMJER2202, Japan. A part of this work was supported by JSPS KAKENHI, grant numbers JP20H05659 and JP19H05788. S. Toyama acknowledges support from a Grant-in-Aid for JSPS Research Fellow, grant number JP20J21517. T.S. acknowledges support from JST-PRESTO, grant number JPMJPR21AA; JSPS KAKENHI, grant number JP20K15014; and the Kazato Research Foundation. A part of this work was supported by the Advanced Research Infrastructure for Materials and Nanotechnology, grant number JPMXP1222UT0044, sponsored by the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Author information

Author notes

  1. Yuya Kanitani, Yoshihiro Kudo & Shigetaka Tomiya

    Present address: Sony Semiconductor Solutions Corporation, Atsugi, Japan

Authors and Affiliations

  1. Institute of Engineering Innovation, School of Engineering, University of Tokyo, Tokyo, Japan

    Satoko Toyama, Takehito Seki, Yuichi Ikuhara & Naoya Shibata

  2. PRESTO, Japan Science and Technology Agency, Kawaguchi, Japan

    Takehito Seki

  3. Sony Group Corporation, Atsugi, Japan

    Yuya Kanitani, Yoshihiro Kudo & Shigetaka Tomiya

  4. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Japan

    Yuichi Ikuhara & Naoya Shibata

  5. Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo, Japan

    Naoya Shibata

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Contributions

S. Toyama, T.S. and N.S. designed the study and wrote the paper. S. Toyama performed the STEM experiments, simulation and image analysis. Y. Kanitani fabricated the transmission electron microscopy samples. Y. Kudo, S. Tomiya and Y.I. contributed to the discussion and comments. N.S. directed the entire study.

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Correspondence to Takehito Seki or Naoya Shibata.

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Extended data

Extended Data Fig. 1 Differential phase contrast (DPC) and tilt-scan-averaged DPC (tDPC) images of the GaN/AlInN heterointerfaces.

a–d, Horizontal and vertical electric field component images, electric field vector color map, and charge density map of the GaN/Al0.81In0.19N (LM-AlInN) sample obtained via tDPC observation along the \(\left[ {{{{\mathrm{11}}}}{\bar{2}}0} \right]\) zone axis. e–h, Horizontal and vertical electric field component images, electric field vector color map, and charge density map of the GaN/ LM-AlInN sample obtained via conventional DPC observation along the \(\left[ {{{{\mathrm{11}}}}{\bar{2}}0} \right]\) zone axis (without tilt averaging). i–l, Horizontal and vertical electric field component images, electric field vector color map and charge density map obtained of the GaN/ LM-AlInN sample via DPC observation along the \(\left[ {1{\bar{1}}{{{\mathrm{00}}}}} \right]\) zone axis (without tilt averaging). m–p, Horizontal and vertical electric field component images, electric field vector color map, and charge density map obtained of the GaN/Al0.88In0.12N (PM-AlInN) sample via DPC observation along the \(\left[ {1{\bar{1}}{{{\mathrm{00}}}}} \right]\) zone axis (without tilt averaging). All scale bars correspond to 20 nm.

Extended Data Fig. 2 Differential phase contrast (DPC) and tilt-scan-averaged DPC (tDPC) profiles.

a, b, Horizontal electric field and charge density profiles of the GaN/Al0.81In0.19N (LM-AlInN) sample obtained via tDPC observation along the \(\left[ {{{{\mathrm{11}}}}{\bar{2}}0} \right]\) zone axis. c, d, Horizontal electric field and charge density profiles of the GaN/ LM-AlInN sample obtained via DPC observation along the \(\left[ {1{\bar{1}}{{{\mathrm{20}}}}} \right]\) zone axis (without tilt averaging). e, f, Horizontal electric field and charge density profiles of the GaN/LM-AlInN sample obtained via DPC observation along the \(\left[ {1{\bar{1}}{{{\mathrm{00}}}}} \right]\) zone axis (without tilt averaging). g, h, Horizontal electric field and charge density profiles of the GaN/Al0.88In0.12N (PM-AlInN) sample obtained via DPC observation along the \(\left[ {1{\bar{1}}{{{\mathrm{00}}}}} \right]\) zone axis (without tilt averaging).

Extended Data Fig. 3 Structure observation of the GaN/PM-AlInN heterostructure.

a, Atomic-resolution high-angle annular dark field STEM image of the GaN/PM-AlInN heterointerface. b, c, d, Indium, Gallium, and Aluminum energy dispersive X-ray spectroscopy elemental maps of the GaN/PM-AlInN heterointerface.

Extended Data Fig. 4 The STEM-EDS line profiles.

a, b STEM-EDS line profiles of LM-AlInN (Fig. 2e–g) and PM-AlInN (Extended Data Fig. 3b–d).

Extended Data Fig. 5 Detector and bright field (BF) disk configuration.

a, Configuration of the bright field disk (green circle) relative to the 40-segmented detector. b, 61-beam-tilt pattern acquired with the detilt coils off. In the actual experiment, these patterns converged into a single BF disk on the detector plane by the detilt coils on.

Extended Data Fig. 6 Simulated results of the tilt averaged BF disks.

a, b Simulated electron channeling patterns of [1-100] and [11–20] incident beam directions with 100 nm sample thickness. The center of the patterns corresponds to the exact zone axis. c, d, 61-beam-tilt patterns extracted from a and b under the experimental conditions of tDPC STEM. e, f, The averaged bright-field disks of the beam-tilt patterns shown in c and d, respectively. a and b, c and d, e and f are set to be the same intensity scales, respectively.

Extended Data Fig. 7 Simulated electric field profiles without high-density n-type donors in the AlInN layers.

a, Simulated electric field profile of GaN/Al0.81In0.19N (LM-AlInN) with n-type donors of 1 × 1016 e/cm−3 in the entire film. b, Simulated electric field profile of GaN/Al0.88In0.12N (PM-AlInN) with n-type donors of 1 × 1016 e/cm−3 in the entire film. c, d, Simulated charge density profiles of the GaN/ LM-AlInN and GaN/PM-AlInN heterointerfaces generated by calculating the divergence of a and b, respectively.

Extended Data Fig. 8 Fitting results of the experimental electric field profiles.

a, Electric field profile of the GaN/Al0.81In0.19N (LM-AlInN) sample along the \(\left[ {1{\bar{1}}{{{\mathrm{00}}}}} \right]\) zone axis by tDPC STEM (blue cross mark) and fitting result based on the Fang-Howard wave function using the Markov chain Monte Carlo optimization (orange line). b, Electric field profile of the GaN/Al0.88In0.12N (PM-AlInN) sample along the \(\left[ {1{\bar{1}}{{{\mathrm{00}}}}} \right]\) zone axis by tDPC STEM (blue crosses) and fitting result based on the same method (orange line).

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Toyama, S., Seki, T., Kanitani, Y. et al. Real-space observation of a two-dimensional electron gas at semiconductor heterointerfaces. Nat. Nanotechnol. 18, 521–528 (2023). https://doi.org/10.1038/s41565-023-01349-8

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