# Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors

Sylvio Rossetti, Aurélien Schmitt, Loubnan Abou-Hamdan, Rémi Bretel, Patrick Bouchon, Emmanuel Baudin, Yannick De Wilde

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Sylvio Rossetti, Aurélien Schmitt, Loubnan Abou-Hamdan, Rémi Bretel, Patrick Bouchon, et al. Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors. EOSAM 2023, Sep 2023, Dijon, France. pp.04003, 10.1051/epjconf/202328704003. hal-04614292

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# Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors

Sylvio Rossetti, Aurélien Schmitt, Loubnan Abou-Hamdan, Rémi Bretel, Patrick Bouchon, Emmanuel Baudin, Yannick De Wilde

<figure><img src="image_2.png" /></figure>

## To cite this version:

Sylvio Rossetti, Aurélien Schmitt, Loubnan Abou-Hamdan, Rémi Bretel, Patrick Bouchon, et al. Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors. EOSAM 2023, Sep 2023, Dijon, France. pp.04003, 10.1051/epjconf/202328704003. hal-04614292

HAL Id: hal-04614292

https://hal.science/hal-04614292v1

Submitted on 17 Jun 2024

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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Distributed under a Creative Commons Attribution 4.0 International License
# Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors

Sylvio Rossetti<sup>1,3,*</sup>, Aurélien Schmitt<sup>2</sup>, Loubnan Abou-Hamdan<sup>1,3</sup>, Rémi Bretel<sup>2</sup>, Patrick Bouchon<sup>3</sup>, Emmanuel Baudin<sup>2</sup>, and Yannick De Wilde<sup>1</sup>.

**Abstract.** In this presentation we will discuss our efforts based on high sensitivity infrared microscopy and spectroscopy to unravel the origin of super-incandescent emission of high-mobility graphene transistors.

## Key-words

Electroluminescence, radiative cooling, near-field spectroscopy

## Introduction

Electroluminescence is a non-thermal radiative process in which a material emits electromagnetic radiation as a response to an electrical current passing through it. If the recombination of electrons and holes giving rise to electroluminescence, can easily be achieved in semi-conductors thanks to their band structure, it is precluded in metals since the electron gas rapidly relaxes to a thermal state. However, we have recently observed that high-quality electrically doped graphene field-effect transistors encapsulated in hexagonal boron nitride (hBN) exhibits a specific behaviour under high bias: the power it emits exceeds the expected one for incandescence.

## High-mobility graphene field-effect transistors (HGFETs) under large bias

Figure 1 shows a schematic representation of an HGFET. The encapsulation of the graphene layer in hBN leads to an enhancement of its flatness, resulting in large electron mobility in the graphene up to ~ 150 000 cm<fnref n="2" />·V⁻<fnref n="1" />·s⁻<fnref n="1" />. The drain and source electrodes allow to apply a longitudinal electric field in the channel of the transistor, whereas the gold backgate permits to tune the electron density in graphene based on capacitor effect.

## Electroluminescence of graphene

We first demonstrate with infrared imaging that the emission exists only in the transistor region. Raman thermometry is then used to rule out the possibility of incandescent emission from optical phonons of graphene. Finally,

<figure><img src="image_2.png" /><figcaption>**Figure 1.** High-mobility field effect graphene transistor. Graphene encapsulated in hBN (light blue) is deposited onto a gold backgate. Drain and source are made of gold electrodes and allow to bias the graphene layer.</figcaption></figure>

we use our recently developed infrared spatial modulation spectroscopy method [1–3] to show that the spectra of the emission exhibit the spectral signature of hyperbolic phonon polaritons of hBN, excited by the electroluminescence in graphene. The amplitude of this feature is such that it largely exceeds that of incandescent emission from hBN.

<figure><img src="image_3.png" /><figcaption>**Figure 2.** Microscope image of a field effect graphene transistor from [4]. The transistor channel, in between two gold electrodes, is partially covered in small gold disks that are essential for near-field infrared spectroscopy.</figcaption></figure>

<footnote n="1"><sup>1</sup>Institut Langevin, ESPCI Paris, Université PSL, CNRS, 1, rue Jussieu, 75005 Paris, France</footnote>

<footnote n="2"><sup>2</sup>Laboratoire de physique de l'ENS, 24, rue Lhomond, 75005 Paris, France</footnote>

<footnote n="3"><sup>3</sup>DOTA, ONERA, 6, chemin de la Vauve aux Granges, 91123 Palaiseau, France</footnote>

<footnote>*e-mail: sylvio.rossetti@espci.fr</footnote>
# Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors

Sylvio Rossetti<sup>1,3,*</sup>, Aurélien Schmitt<sup>2</sup>, Loubnan Abou-Hamdan<sup>1,3</sup>, Rémi Bretel<sup>2</sup>, Patrick Bouchon<sup>3</sup>, Emmanuel Baudin<sup>2</sup>, and Yannick De Wilde<sup>1</sup>.

**Abstract.** In this presentation we will discuss our efforts based on high sensitivity infrared microscopy and spectroscopy to unravel the origin of super-incandescent emission of high-mobility graphene transistors.

## Key-words

Electroluminescence, radiative cooling, near-field spectroscopy

## Introduction

Electroluminescence is a non-thermal radiative process in which a material emits electromagnetic radiation as a response to an electrical current passing through it. If the recombination of electrons and holes giving rise to electroluminescence, can easily be achieved in semi-conductors thanks to their band structure, it is precluded in metals since the electron gas rapidly relaxes to a thermal state. However, we have recently observed that high-quality electrically doped graphene field-effect transistors encapsulated in hexagonal boron nitride (hBN) exhibits a specific behaviour under high bias: the power it emits exceeds the expected one for incandescence.

## High-mobility graphene field-effect transistors (HGFETs) under large bias

Figure 1 shows a schematic representation of an HGFET. The encapsulation of the graphene layer in hBN leads to an enhancement of its flatness, resulting in large electron mobility in the graphene up to ~ 150 000 cm<fnref n="2" />·V⁻<fnref n="1" />·s⁻<fnref n="1" />. The drain and source electrodes allow to apply a longitudinal electric field in the channel of the transistor, whereas the gold backgate permits to tune the electron density in graphene based on capacitor effect.

## Electroluminescence of graphene

We first demonstrate with infrared imaging that the emission exists only in the transistor region. Raman thermometry is then used to rule out the possibility of incandescent emission from optical phonons of graphene. Finally,

<figure><img src="image_4.png" /><figcaption>**Figure 1.** High-mobility field effect graphene transistor. Graphene encapsulated in hBN (light blue) is deposited onto a gold backgate. Drain and source are made of gold electrodes and allow to bias the graphene layer.</figcaption></figure>

we use our recently developed infrared spatial modulation spectroscopy method [1–3] to show that the spectra of the emission exhibit the spectral signature of hyperbolic phonon polaritons of hBN, excited by the electroluminescence in graphene. The amplitude of this feature is such that it largely exceeds that of incandescent emission from hBN.

<figure><img src="image_5.png" /><figcaption>**Figure 2.** Microscope image of a field effect graphene transistor from [4]. The transistor channel, in between two gold electrodes, is partially covered in small gold disks that are essential for near-field infrared spectroscopy.</figcaption></figure>

<footnote n="1"><sup>1</sup>Institut Langevin, ESPCI Paris, Université PSL, CNRS, 1, rue Jussieu, 75005 Paris, France</footnote>

<footnote n="2"><sup>2</sup>Laboratoire de physique de l'ENS, 24, rue Lhomond, 75005 Paris, France</footnote>

<footnote n="3"><sup>3</sup>DOTA, ONERA, 6, chemin de la Vauve aux Granges, 91123 Palaiseau, France</footnote>

<footnote>*e-mail: sylvio.rossetti@espci.fr</footnote>
Figure 2 is a microscope image of an HGFET chan-
nel between two gold electrodes. Small gold disks are de-
posited over the encapsulated graphene region and play the
role of scatterers of the near-field to the far-field. This fea-
ture is essential to achieve spectroscopy of the near-field
modes of hyperbolic phonon polaritons of hBN.

Conduction mechanism and interpretation

The achievement of electroluminescent graphene is
closely related to interband Zener-Klein tunneling, which
is a conduction mechanism involving interband transitions
in which electron-hole pairs are formed under an intense
electric field, producing a strongly non-equilibrium elec-
tronic distribution. In such condition, an efficient cool-
ing mechanism of the electron gas occurs through the ex-
citation of hyperbolic phonon polaritons in hBN as re-
cently observed by some of us in high mobility field-effect
graphene transistors [5, 6].

Acknowledgment

The research leading to these results has received partial
funding from the European Union Horizon 2020 research
and innovation program under grant agreement No.881603

"Graphene Core 3", and from the French ANR-21-CE24-
0025-01 "ELuSeM". This work also received financial
support from LABEX WIFI (Laboratory of Excellence
within the French Program "Investments for the Future")
under references ANR-10-LABX-24 and ANR-10-IDEX-
0001-02 PSL.

References

[1] C. Li, V. Krachmalnicoff, P. Bouchon, J. Jaeck, N. Bardou, R. Haidar, Y. De Wilde, Physical Review Letters **121**, 243901 (2018)

[2] L. Abou-Hamdan, C. Li, R. Haidar, V. Krachmalnicoff, P. Bouchon, Y. De Wilde, Optics Letters **46**, 981 (2021)

[3] L. Abou-Hamdan, L. Coudrat, S. Bidault, V. Krach-
malnicoff, R. Haïdar, P. Bouchon, Y. De Wilde, ACS
Photonics **9**, 2295 (2022)

[4] L. Abou-Hamdan, Ph.D. thesis, Institut Langevin - Université PSL (2023)

[5] E. Baudin, C. Voisin, B. Plaçais, Advanced Functional Materials **30**, 1904783 (2020)

[6] W. Yang, S. Berthou, X. Lu, Q. Wilmart, A. Denis, M. Rosticher, T. Taniguchi, K. Watanabe, G. Fève, J.M. Berroir et al., Nature Nanotechnology **13**, 47 (2018)
Figure 2 is a microscope image of an HGFET chan-
nel between two gold electrodes. Small gold disks are de-
posited over the encapsulated graphene region and play the
role of scatterers of the near-field to the far-field. This fea-
ture is essential to achieve spectroscopy of the near-field
modes of hyperbolic phonon polaritons of hBN.

Conduction mechanism and interpretation

The achievement of electroluminescent graphene is
closely related to interband Zener-Klein tunneling, which
is a conduction mechanism involving interband transitions
in which electron-hole pairs are formed under an intense
electric field, producing a strongly non-equilibrium elec-
tronic distribution. In such condition, an efficient cool-
ing mechanism of the electron gas occurs through the ex-
citation of hyperbolic phonon polaritons in hBN as re-
cently observed by some of us in high mobility field-effect
graphene transistors [5, 6].

Acknowledgment

The research leading to these results has received partial
funding from the European Union Horizon 2020 research
and innovation program under grant agreement No.881603

"Graphene Core 3", and from the French ANR-21-CE24-
0025-01 "ELuSeM". This work also received financial
support from LABEX WIFI (Laboratory of Excellence
within the French Program "Investments for the Future")
under references ANR-10-LABX-24 and ANR-10-IDEX-
0001-02 PSL.

**References**

[1] C. Li, V. Krachmalnicoff, P. Bouchon, J. Jaeck, N. Bardou, R. Haidar, Y. De Wilde, Physical Review Letters **121**, 243901 (2018)

[2] L. Abou-Hamdan, C. Li, R. Haidar, V. Krachmalni-coff, P. Bouchon, Y. De Wilde, Optics Letters **46**, 981 (2021)

[3] L. Abou-Hamdan, L. Coudrat, S. Bidault, V. Krach-
malnicoff, R. Haïdar, P. Bouchon, Y. De Wilde, ACS
Photonics **9**, 2295 (2022)

[4] L. Abou-Hamdan, Ph.D. thesis, Institut Langevin - Université PSL (2023)

[5] E. Baudin, C. Voisin, B. Plaçais, Advanced Functional Materials **30**, 1904783 (2020)

[6] W. Yang, S. Berthou, X. Lu, Q. Wilmart, A. Denis, M. Rosticher, T. Taniguchi, K. Watanabe, G. Fève, J.M. Berroir et al., Nature Nanotechnology **13**, 47 (2018)