# Stress and doping analysis of low n-doped GaN layers grown on GaN, silicon and sapphire substrates by micro-Raman 2. Physics and characterization

Ndembi Ignoumba-Ignoumba, Camille Sonneville, Adrien Bidaud, Mohammed El Amrani, Thibaud Guillemin, Maroun Dagher, Vishwajeet Maurya, Florian Bartoli, Eric Frayssinet, Farid Medjdoub, et al.

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Ndembi Ignoumba-Ignoumba, Camille Sonneville, Adrien Bidaud, Mohammed El Amrani, Thibaud Guillemin, et al.. Stress and doping analysis of low n-doped GaN layers grown on GaN, silicon and sapphire substrates by micro-Raman 2. Physics and characterization. ICNS-15 - the 15th International Conference on Nitride Semiconductors, Jul 2025, Malmö, Sweden. hal-05097968

HAL Id: hal-05097968

https://hal.science/hal-05097968v1

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# Stress and doping analysis of low n-doped GaN layers grown on GaN, silicon and sapphire substrates by micro-Raman

## 2. Physics and characterization

Ndembi Ignoumba-Ignoumba¹, **Camille Sonneville**¹, Adrien Bidaud², Mohammed El Amrani³, Thibaud Guillemin⁴, Maroun Dagher⁵, Vishwajeet Maurya³, Florian Bartoli⁴, Eric Frayssinet⁴, Farid Medjdoub², Julien Buckley³, Yvon Cordier⁴, Matthew Charles³, Dominique Planson¹, Cyril Buttay¹

¹ Univ. Lyon, INSA Lyon, Univ. Claude Bernard Lyon 1, Ecole Centrale Lyon, CNRS, Ampère, F-69621, France.

² I.E.M.N - CNRS, 59652 Villeneuve d'Ascq, France.

³ Univ. Grenoble Alpes, CEA-LETI, Grenoble 38000, France.

⁴ Université Côte d'Azur, CNRS, CRHEA, F-06560 Valbonne, France.

⁵ INSA Lyon, Ecole Centrale de Lyon, CNRS, Université Claude Bernard Lyon 1, CPE Lyon, INL, UMR5270, 69621, Villeurbanne, France.

## Abstract text

Vertical GaN power devices counters the drawbacks of the lateral ones. The best performances are observed with vertical GaN-on-GaN, but the absence of large GaN substrates makes the homoepitaxy option less marketable than the heteroepitaxy one. However, thick heteroepitaxial GaN drift layers must exhibit a low biaxial stress and a low n-doping density. Monitoring these properties of GaN layers are therefore crucial issues for vertical GaN power devices development. Here, a methodology is proposed, using non-destructive micro-Raman, to analyze biaxial stress and n-doping density for low n-doped GaN layers (< $10^{17}$ cm⁻³) independently of the substrate type (GaN, silicon and sapphire).

The variation of $A_1(LO)$ and $E_2^H$ GaN Raman shifts ($\omega_{A1}$, $\omega_{E2}$) due to biaxial stress ($\sigma_B$) and the n-doping density ($n$) is $\Delta\omega_{A1} = K_{A1}^B \times \sigma_B + f(n)$ and $\Delta\omega_{E2} = K_{E2}^B \times \sigma_B$. Combining these two equations, $\omega_{A1}$ can be linearly correlated to $\omega_{E2}$, with a slope ($S=K_{A1}^B/K_{E2}^B$) independent of the biaxial stress and a y-intercept $g(n)$ increasing with $n$. Micro-Raman 2D-mapping shows that samples display the expected behavior concerning the biaxial stress: GaN-on-sapphire layers exhibit the highest values of the $\omega_{A1}$ and $\omega_{E2}$ (compressive stress) while GaN-on-silicon layers have the lowest ones (tensile stress). In addition, results agree with the proposed relationship between $\omega_{A1}$ and $\omega_{E2}$, such that regardless of the substrate, the slope $S$ is similar. Hence, this work refines $S$ to $0.78 \pm 0.03$, compared to the literature (0.28 to 0.80 [1,2]). Moreover, as expected, the y-intercept increases with the sample n-doping level, regardless of its substrate. Present results can then be used as a benchmark for estimating n-doping level and inhomogeneity of low n-doped GaN layers.

This study shows that micro-Raman is an effective technique for analyzing the low doped and low strain layers required for the next generation of vertical GaN power devices. Furthermore, the final publication will correlate these micro-Raman results with other electrical and physical characterizations.

This work is funded by the French ANR, Grant No: ANR-22-PEEL-0004, ANR-11-LABX-0014, ANR-11-LABX-0014.

[1] F. Demangeot, et al., MRS Internet j. nitride semicond. res., vol. 1, p. e23, 1996, doi: 10.1557/S1092578300001952.

[2] J.-M. Wagner et al., Phys. Rev. B, vol. 66, no. 11, p. 115202, Sep. 2002, doi: 10.1103/PhysRevB.66.115202.