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Electric field mapping of wide-bandgap semiconductor devices at a submicrometre resolution

Abstract

Electric fields drive the degradation of wide-bandgap semiconductor devices. However, directly mapping the electric field inside an active device region remains challenging. Here we show that electric-field-induced second harmonic generation can be used to map the electric field in the device channel of GaN-based high-electron-mobility transistors at submicrometre resolution. To illustrate the capabilities of the approach, we use it to examine the impact of carbon impurities in the epitaxial buffer layer of a device. Carbon is a p dopant in GaN, and small changes in its concentration can dramatically change the bulk Fermi level, sometimes resulting in a floating buffer that is ‘short-circuited’ to the device channel via dislocations. Our measurements show that very different electric field distributions can occur in devices with different carbon concentrations, despite them having similar device terminal characteristics. We also show that dislocation-related leakage paths can lead to inhomogeneity in the electric field.

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Fig. 1: Schematic of the EFISHG experiment on GaN HEMTs and device information.
Fig. 2: Electric field distribution in GaN HEMT devices.
Fig. 3: Simulation results for devices on wafer A and B.
Fig. 4: Simulated channel in-plane electric field Ex averaged over the lateral spatial resolution of the EFISHG measurement.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Code availability

The custom-developed codes for the SILVACO Atlas simulation, LabView data acquisition and MATLAB data analysis are available from the corresponding author upon reasonable request.

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Acknowledgements

We acknowledge financial contribution from the Engineering and Physical Sciences Research Council (EPSRC) under grant EP/R022739/1. Y.C. acknowledges the China Scholarship Council for financial support under grant 201806290005. The GaN HEMTs were provided by T. Martin, IQE Europe, and their fabrication at BeMiTec was funded by the European Space Agency.

Author information

Affiliations

Authors

Contributions

J.W.P. and M.K. conceived the idea for the project. Y.C. designed the EFISHG set-up and experimental procedure, conducted the experiments and analysed the results. J.W.P. provided important expertise on the technique. F.Y. conducted the simulation. M.J.U. provided significant input on the interpretation of data. All authors participated in the scientific discussion. Y.C. wrote the manuscript with the assistance of J.W.P., M.J.U. and M.K. M.K. supervised the project.

Corresponding author

Correspondence to Martin Kuball.

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Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Electronics thanks Ilan Shalish and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Schematic of optical setup for the EFISHG measurement.

Abbreviations for optical components: OC – optical chopper; HWP – half waveplate; LP – linear polarizer; SD – short-pass dichroic mirror; BS – beam splitter; SF – short-pass filter; APD – avalanche photodetector.

Extended Data Fig. 2 Lateral spatial resolution of the setup.

a, Fundamental laser intensity reflected from the sample around a knife edge to determine spatial resolution of the optical system used (50× magnification 0.5NA objective lens). b, line spread function, that is differential of the intensity shown in a, gives the lateral resolution. The measured lateral resolution is (765±35) nm.

Source data

Extended Data Fig. 3 Buffer doping and band diagram of two wafers.

a, SIMS iron (Fe) and carbon (C) profile of wafers A and B; overlaid are simplified doping density profiles subsequently used for the device simulation33 (Supplementary Table 1). Carbon is assumed to be primarily situated on the nitrogen site (CN). b, Unbiased band profile from the device surface into the epilayer on wafer A and wafer B.

Source data

Extended Data Fig. 4 EFISHG measurement in GaN HEMT devices.

a, b, SHG signal (top panel) and reflectance (bottom panel) from source to drain contact of the GaN-on-SiC HEMT in the OFF state (VGS=−6V) under different gate-drain bias voltages VDG for wafer A and wafer B, respectively.

Source data

Extended Data Fig. 5 Quantitative calibration of the electric field Ex extracted from EFISHG measurement.

a, b, Potential difference between source and drain contact, obtained by integrating the electric field Ex, determined from the SHG signal in Extended Data Fig. 4 for wafer A and wafer B, respectively. Insert shows the potential profiles from the source contact edge located at x = 0 µm towards the drain contact edge located at x = 5.5 µm. The proportionality factor α in equation (2) was adjusted to 2.1 for wafer A so that the potential matches the applied VDG, and to 3.4 for wafer B, to match the applied VDG up to 111V.

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–7, Table 1 and Notes 1–3.

Source data

Source Data Fig. 1

Statistical source data.

Source Data Fig. 2

Statistical source data.

Source Data Fig. 3

Statistical source data.

Source Data Fig. 4

Statistical source data.

Source Data Extended Data Fig. 2

Statistical source data.

Source Data Extended Data Fig. 3

Statistical source data.

Source Data Extended Data Fig. 4

Statistical source data.

Source Data Extended Data Fig. 5

Statistical source data.

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Cao, Y., Pomeroy, J.W., Uren, M.J. et al. Electric field mapping of wide-bandgap semiconductor devices at a submicrometre resolution. Nat Electron 4, 478–485 (2021). https://doi.org/10.1038/s41928-021-00599-5

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