Structural, Morphological, Vibrational and Optical Properties of GaN Films Grown by Reactive Sputtering: The Effect of RF Power at Low Working Pressure Limit

This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.

Keywords:
GaN; reactive sputtering; thin film

Authorship

R. S. de Oliveira

Instituto Tecnológico de Aeronáutica (ITA), Laboratório de Plasmas e Processos (LPP), São José dos Campos, SP, Brasil.Instituto Tecnológico de AeronáuticaBrasilSão José dos Campos, SP, BrasilInstituto Tecnológico de Aeronáutica (ITA), Laboratório de Plasmas e Processos (LPP), São José dos Campos, SP, Brasil.

H. A. Folli

C. Stegemann

Faculdade de Tecnologia SENAI Jaraguá do Sul, Jaraguá do Sul, SC, Brasil.Faculdade de Tecnologia SENAI Jaraguá do SulBrasilJaraguá do Sul, SC, BrasilFaculdade de Tecnologia SENAI Jaraguá do Sul, Jaraguá do Sul, SC, Brasil.

I. M. Horta

B. S. Damasceno

W. Miyakawa

Instituto de Estudos Avançados (IEAv), São José dos Campos, SP, Brasil.Instituto de Estudos AvançadosBrasilSão José dos Campos, SP, BrasilInstituto de Estudos Avançados (IEAv), São José dos Campos, SP, Brasil.

A. L. J. Pereira

M. Massi

Universidade Presbiteriana Mackenzie, Escola de Engenharia (PPGEMN), São Paulo, SP, Brasil.Universidade Presbiteriana MackenzieBrasilSão Paulo, SP, BrasilUniversidade Presbiteriana Mackenzie, Escola de Engenharia (PPGEMN), São Paulo, SP, Brasil.

https://orcid.org/0000-0002-7117-8039

A. S. da Silva Sobrinho

https://orcid.org/0000-0001-7227-9176

D. M. G. Leite ^**e-mail: leite@ita.br

https://orcid.org/0000-0002-1792-6171

*e-mail: leite@ita.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (10)
Tables (1)

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Figure 1
Schematic representation of the deposition chamber, showing the cylindrical magnetron and the substrate holder.

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Figure 2
Curves of film thickness as function of (a) the working pressure and (b) the RF power. The error bar was smaller than the plotting point size.

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Figure 3
X-ray diffractograms of the GaN/Si films grown at different working pressures. The Si substrate narrow peaks are observed at ~33 and ~62 degrees. The film thicknesses are also indicated on the curves.

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Figure 4
(a) X-ray diffractograms of the GaN/Si films grown using different RF power. (b) Expanded scale in the interval 30° - 40°, showing the main diffraction peaks and respective expected degree positions (vertical dashed lines), according to Schulz and Thiemann³²32 Schulz H, Thiemann KH. Crystal structure refinement of AlN and GaN. Solid State Commun [Internet]. 1977 Sep 1 [cited 2019 Nov 11];23(11):815-9. Available from: https://www.sciencedirect.com/science/article/pii/0038109877909590.
https://www.sciencedirect.com/science/ar... .

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Figure 5
(a) Lattice parameters a (circles, right axis) and c (squares, left axis). The horizontal dashed arrows indicate the respective values for relaxed GaN according to¹1 Leszczynski M, Teisseyre H, Suski T, Grzegory I, Bockowski M, Jun J, et al. Lattice parameters of gallium nitride. Appl Phys Lett. 1996;69(1):73-5. http://dx.doi.org/10.1063/1.118123.
http://dx.doi.org/10.1063/1.118123... ; (b) c/a lattice parameter ratio (squares, left axis) and the (0002) peak relative intensity (circles, right axis). The horizontal dashed arrows indicate the c/a value for epitaxial GaN according to¹1 Leszczynski M, Teisseyre H, Suski T, Grzegory I, Bockowski M, Jun J, et al. Lattice parameters of gallium nitride. Appl Phys Lett. 1996;69(1):73-5. http://dx.doi.org/10.1063/1.118123.
http://dx.doi.org/10.1063/1.118123... ; (c) (0002) and (1011) peaks FWHM versus applied RF powers.

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Figure 6
AFM and SEM topography images of GaN deposited on Si (100) at (a,d) 30 W, (b,e) 60 W and (c,f) 90 W, respectively.

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Figure 7
Raman spectra for samples deposited using 0.40 Pa working pressure, with different RF powers. Expected peak position for E₂(H) and A₁(LO) phonon modes are shown using dashed lines.

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Figure 8
Ellipsometry parameters I_S and I_C (points) and fitted curves (lines) as a function of the photon energy for three representative samples grown at 0.40 Pa and (a) 30, (b) 60 and (c) 90 W. The vertical arrows indicate the resulting gap energy (E_g) after proper modeling fit. The total thickness of the film (h) as well as the thickness of the top layer (dh) used to simulate the roughness (composed by 50% GaN + 50% air) are also displayed in the respective graphs.

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Figure 9
Curves of (a) refraction index dispersion n and (b) extinction coefficient k versus photon energies for representative samples.

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Figure 10
Band-gap energy (E_g) versus the RF power, for the samples grown at 0.40 Pa together with that grown with 1.33 Pa (60 W). The horizontal arrow indicates the expected E_g value for epitaxial GaN³⁹39 Muth J, Johnson M, Kolbas RM. Absorption coefficient and refractive index of GaN, AIN and AlGaN alloys. Mat Res Soc Symp Proc. 1999;537:G5.2..

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Table 1
R_a, R_ms, and R_z roughness parameters calculated from the AFM images.

Figure 1 Schematic representation of the deposition chamber, showing the cylindrical magnetron and the substrate holder.

Figure 2 Curves of film thickness as function of (a) the working pressure and (b) the RF power. The error bar was smaller than the plotting point size.

Figure 3 X-ray diffractograms of the GaN/Si films grown at different working pressures. The Si substrate narrow peaks are observed at ~33 and ~62 degrees. The film thicknesses are also indicated on the curves.

Figure 4 (a) X-ray diffractograms of the GaN/Si films grown using different RF power. (b) Expanded scale in the interval 30° - 40°, showing the main diffraction peaks and respective expected degree positions (vertical dashed lines), according to Schulz and Thiemann³²32 Schulz H, Thiemann KH. Crystal structure refinement of AlN and GaN. Solid State Commun [Internet]. 1977 Sep 1 [cited 2019 Nov 11];23(11):815-9. Available from: https://www.sciencedirect.com/science/article/pii/0038109877909590.
https://www.sciencedirect.com/science/ar... .

Figure 5 (a) Lattice parameters a (circles, right axis) and c (squares, left axis). The horizontal dashed arrows indicate the respective values for relaxed GaN according to¹1 Leszczynski M, Teisseyre H, Suski T, Grzegory I, Bockowski M, Jun J, et al. Lattice parameters of gallium nitride. Appl Phys Lett. 1996;69(1):73-5. http://dx.doi.org/10.1063/1.118123.
http://dx.doi.org/10.1063/1.118123... ; (b) c/a lattice parameter ratio (squares, left axis) and the (0002) peak relative intensity (circles, right axis). The horizontal dashed arrows indicate the c/a value for epitaxial GaN according to¹1 Leszczynski M, Teisseyre H, Suski T, Grzegory I, Bockowski M, Jun J, et al. Lattice parameters of gallium nitride. Appl Phys Lett. 1996;69(1):73-5. http://dx.doi.org/10.1063/1.118123.
http://dx.doi.org/10.1063/1.118123... ; (c) (0002) and (1011) peaks FWHM versus applied RF powers.

Figure 6 AFM and SEM topography images of GaN deposited on Si (100) at (a,d) 30 W, (b,e) 60 W and (c,f) 90 W, respectively.

Figure 7 Raman spectra for samples deposited using 0.40 Pa working pressure, with different RF powers. Expected peak position for E₂(H) and A₁(LO) phonon modes are shown using dashed lines.

Figure 8 Ellipsometry parameters I_S and I_C (points) and fitted curves (lines) as a function of the photon energy for three representative samples grown at 0.40 Pa and (a) 30, (b) 60 and (c) 90 W. The vertical arrows indicate the resulting gap energy (E_g) after proper modeling fit. The total thickness of the film (h) as well as the thickness of the top layer (dh) used to simulate the roughness (composed by 50% GaN + 50% air) are also displayed in the respective graphs.

Figure 9 Curves of (a) refraction index dispersion n and (b) extinction coefficient k versus photon energies for representative samples.

Figure 10 Band-gap energy (E_g) versus the RF power, for the samples grown at 0.40 Pa together with that grown with 1.33 Pa (60 W). The horizontal arrow indicates the expected E_g value for epitaxial GaN³⁹39 Muth J, Johnson M, Kolbas RM. Absorption coefficient and refractive index of GaN, AIN and AlGaN alloys. Mat Res Soc Symp Proc. 1999;537:G5.2..

Table 1 R_a, R_ms, and R_z roughness parameters calculated from the AFM images.

RF power	R_a (nm)	R_ms (nm)	R_z (nm)
30 W	2.92 ± 0.36	5.97 ± 0.16	29.5 ± 1.1
60 W	3.02 ± 0.18	3.83 ± 0.23	16.3 ± 1.5
90 W	4.88 ± 0.20	6.22 ± 0.23	28.5 ± 1.9

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Structural, Morphological, Vibrational and Optical Properties of GaN Films Grown by Reactive Sputtering: The Effect of RF Power at Low Working Pressure Limit

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[1] *e-mail: leite@ita.br