# Nanostructuring of 4H-SiC by high temperature annealing

Enora Marion Vuillermet, Elise Usureau, Mihai Lazar, Regis Deturche

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Enora Marion Vuillermet, Elise Usureau, Mihai Lazar, Regis Deturche. Nanostructuring of 4H-SiC by high temperature annealing. 19th International Conference on Silicon Carbide and Related Materials (ICSCRM 2022), Sep 2022, Davos, Switzerland. . hal-04171193

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Submitted on 26 Jul 2023

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# Nanostructuring of 4H-SiC by high temperature annealing

E. Vuillermet¹*, E. Usureau¹, M. Lazar¹+, R. Deturche¹

¹Laboratory Light, Nanomaterials & Nanotechnologies, CNRS EMR 7004, University of Technology of Troyes, 12 rue Marie Curie, 10004 Troyes, France

*enora.vuillermet@utt.fr, +mihai.lazar@utt.fr

## 1 Introduction

SiC high refractive index (2.65 at 590 nm) compared to air causes **low extraction efficiency of light emission** [1]. The objective of the project is to improve the extraction of light in 4H-SiC by changing the morphology of its surface. **High temperature annealing** is used to nanostructure 4H-SiC by controlling the sublimation of Si in surface. **PiN diode structures** are then developed.

## 2 Nanostructuring the surface of 4H-SiC

→ Annealing of 4H-SiC in the **AET furnace** with high temperature (up to 1900°C) rapid (2°C/s) temperature process (**RTP**) in Ar.

<figure><img src="image_2.png" /><figcaption>Temperature and Pressure profiles for 30min 1700°C annealing</figcaption></figure>

<figure><img src="image_3.png" /></figure>

→ **Nanostructuring** of the surface after high temperature annealing

<figure><img src="image_4.png" /><figcaption>Mean surface roughness (rms) after annealing</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>AFM analysis of 1700°C annealed surface</figcaption></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

* The surface morphology of 4H-SiC becomes **needle-shaped**, like black silicon [2], after high temperature annealing.

* Si sublimation during high temperature annealing leads to a slight **etching** of the surface.

## 3 Fabrication of PiN diode structures

→ **Electrically isolated PiN diode structures** with a **nanostructured** surface are developed.

<figure><img src="image_8.png" /></figure>

## 4 Electroluminescence of the PiN diode structures

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>Off-axis</figcaption></figure>

<caption>On-axis</caption>

→ **Ohmic contacts** :

* C face : Ti / Ni → 10 / 120nm

* Si face : Ni/Ti/Al/Ni → 11/25/150/11nm

* RTA annealing: 800-900°C / 90s

→ The electro-luminescence of the PiN diode structures is **blue**.

## 5 Conclusion

* The surface of 4H-SiC is **nanostructured** and present a **needle-shape** surface morphology for annealing at higher temperatures (1700 and 1600°C).

* Electrical measurements show an **electro-luminescence** of the PiN diode structures under a **forward bias of 8V**. The off-axis sample has a better luminescence than the on-axis one but we don't observe any difference of luminescence when the high temperature annealing changes from 1500°C to 1700°C.

* Further spectral analysis of this luminescence will be made to determine if it varies depending on the annealing temperature of the diodes.

## References

1. Y. Ou, V. Jokubavicius, M. Kaiser, P. Wellmann, M. K. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, Fabrication of Broadband Antireflective Sub-Wavelength Structures on Fluorescent SiC, Materials Science Forum, 740, 1024-1027, 2013.

2. X. Liu, P. R. Coxon, M. Peters, B. Hoex, J. M. Cole, and D. J. Fray, Black silicon: fabrication methods, properties and solar energy applications, Energy Environ. Sci. 7, 3223-3263, 2014.

## Acknowledgements

We would like to thank Linkoping University (LIU) for the growth of the 4H-SiC epitaxial layers.