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# Dynamic RDS-on degradation analysis on power GaN HEMT by means of TCAD simulations and experimental measurement

Gaëtan Toulon, Cristina Miccoli, David Trémouilles, Frédéric Morancho,
Maria-Eloisa Castagna, Alessandro Chini, Ferdinando Iucolano

► To cite this version:

Gaëtan Toulon, Cristina Miccoli, David Trémouilles, Frédéric Morancho, Maria-Eloisa Castagna, et al.. Dynamic RDS-on degradation analysis on power GaN HEMT by means of TCAD simulations and experimental measurement. WOCSDICE - EXMATEC 2023 6th Workshop on Compound Semiconductor Devices and Integrated Circuits held in Europe 17th Expert Evaluation and Control of Compound Semiconductor Materials and Technologies, May 2023, Palerme, Italy. hal-04128305

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Submitted on 14 Jun 2023

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# Dynamic R<sub>DS-on</sub> degradation analysis on power GaN HEMT by means of TCAD simulations and experimental measurement.

Gaëtan Toulon¹, Cristina Miccoli², David Tremouilles³, Frédéric Morancho³, Maria-Eloisa Castagna², Alessandro Chini⁴,
Ferdinando Iucolano²

¹STMicroelectronics, 51 Rue de l'Innovation, 31670 Labège, France

²STMicroelectronics, 95121 Catania, Italy

³LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse, France

⁴Department of Engineering “Enzo Ferrari,” Università di Modena e Reggio Emilia, 41125 Modena, Italy
gaetan.toulon@st.com

## Abstract

This paper deals with the dynamic R<sub>DS-on</sub> degradation of GaN HEMT for 650V application. An overview of different parameters impacting the performances of the devices were investigated experimentally. From temperature dependent characterisations the main trap at the origin of the degradation could be extracted. The signature of carbon in the GaN buffer could be confirmed by TCAD simulation, where the same trends were reproduced.

## Introduction

Gallium Nitride (GaN) high electron mobility transistors (HEMTs) has been widely accepted in power application due to their high current and voltage capabilities. However, due to the nature of hetero epitaxy, the GaN present numerous defects that can impact the electrical performances of the devices [1], such as the well-known on-resistance (R<sub>DS-on</sub>) degradation [2]. This effect has been widely documented and many trap signatures were extracted [3, 4]. In order to sustain the high voltage and limit the leakage currents in the GaN buffer, iron (Fe) or carbon is introduced [5]. However, the introduction of these species generates traps that could affect the RDS-on performance.

In this paper, we deal with the evaluation of RDS-on degradation on GaN HEMT for 650V applications by monitoring the RDS-on recovery following a high voltage stress. The performance degradation, attributed to carbon, could be reproduced by TCAD simulations.

## Experimental setup

Experimental characterizations were performed on D-mode power AlGaN/GaN HEMT for 650V applications on 8 inches wafer on Silicon substrate. The tests were performed with the high voltage / high current fast switch (N1267a) option of the Keysight B1505a associated to a semiautomatic probing station. Temperature control was possible thank to the thermally regulated chuck.

We were able to monitor the R<sub>DS-on</sub> variation of the HEMT after an off-state drain bias for different conditions: drain bias, stress duration and temperature.

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** R<sub>DS-on</sub> variation after a stress of 1min at different off-state drain biases</figcaption></figure>

## Experimental results

Figure 1, representing the R<sub>DS-on</sub> variation at 100°C after a stress of one minute shows a degradation of R<sub>DS-on</sub> several time higher than static value (“1V”). The degradation is more pronounced at lower V<sub>DS</sub> stress (100 and 150V) with a recovery in the order of ten seconds and is less pronounced at higher stress voltage.

<figure><img src="image_3.png" /><figcaption>**Fig. 2.** RDS-on variation after a stress of V<sub>DS</sub>=100V for 1min at different temperatures</figcaption></figure>

Figure 2 presents the R<sub>DS-on</sub> recovery for a 100V stress at different temperature. A higher RDS-on value just after the stress and an accelerated recovery at higher temperature is a sign of a thermally activated mechanism. On Figure 2 is also represented the derivative of the R<sub>DS-on</sub> as a function of log(t). The curves show a minimum corresponding to the main time constant of the R<sub>DS-on</sub> recovery.

From the time constant extracted at different temperatures, we could extract an activation energy of 0.88eV (figure 3). This energy should be assigned as a carbon related trap that is present inside the buffer layer [6, 7].

## Simulations

TCAD simulations were performed with same electrical conditions to reproduce the R<sub>DS-on</sub> degradation observed experimentally. Acceptor with activation energy of 0.9eV from valence band were used in the GaN buffer; the trap capture cross section was used as a fitting parameter. This buffer is partially compensated by shallow donor, modelized by N-type doping.

We also used the standard piezo-electric polarization model based on Ambacher [8] theory, as well as SRH recombination for traps.

We also considered the temperature dependence mobility degradation due to phonon scattering.
<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Arrhenius plot from main trap mechanism: measurement with activation energy, and simulation</figcaption></figure>

Figure 4 shows the transient of simulated R<sub>DS-on</sub> after a stress of 100V for different temperatures. Same trends could be observed with measurements in terms of variation with time and amplitude. Maximum degradation magnitude was adjusted to experimental data by varying the acceptor traps concentration in the GaN buffer.

<figure><img src="image_5.png" /><figcaption>**Fig. 4.** Simulated R<sub>DS-on</sub> recovery after a drain stress of 100V for 1min.</figcaption></figure>

From derivative spectrum also represented figure 4, we were able to represent the results on the Arrhenius plot on figure 3. Good fit with measurement can be observed, confirming the origin of the trap that is the cause of the main R<sub>DS-on</sub> degradation.

## Conclusions

On this paper, we analysis the R<sub>DS-on</sub> degradation on power HEMT by means of characterizations and simulations The measurement on different biases and temperatures allowed us to identify the worst stress conditions for dynamic R<sub>DS-on</sub> degradation and thanks to simulations, we were able to identify the cause.

Thank to this analysis, we have now a better understanding of the mechanisms of the R<sub>DS-on</sub> degradation. With the help of TCAD simulations, we could improve the transistor design to mitigate this effect.

## Acknowledgments

This work was supported by the LAAS-CNRS PROOF platform, partly financed by the Occitanie region

## References

[1] J. A. del Alamo, et al., *IEEE Trans. Electron Devices*, **66**, 4578–4590 (2019).

[2] E. Canato et al., *Microelectron. Rel.*, 113841 (2020).

[3] D. Bisi et al., *IEEE Trans. Electron Devices*, **60**, 3166–3175 (2013).

[4] D. Johnstone, Proceedings of SPIE - The International Society for Optical Engineering, 6473 (2007)

[5] H. Yacoub et al., *IEEE Trans. Electron Devices*, **65**, 3192-3197 (2018).

[6] C. H. Seager et al., *Journal of Applied Physics*, **92**, 6553-6560 (2002)

[7] P. Boguslawski et al., Appl. Phys. Letter, **69**, 233-235 (1996)

[8] O. Ambacher et al., *Journal of Applied Physics*, **85**, 3222-3233 (1999)