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Temperature-Dependent Raman and Spectroscopic Ellipsometry Analysis of MOCVD-Grown GaN/Si (111) Heterostructures With and Without Al2O3 Interlayers.

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Title: Temperature-Dependent Raman and Spectroscopic Ellipsometry Analysis of MOCVD-Grown GaN/Si (111) Heterostructures With and Without Al2O3 Interlayers.
Authors: Nafisa, Manika Tun1 (AUTHOR) mnafisa@students.kennesaw.edu, Rahman, S M Atiqur1 (AUTHOR), Feng, Zhe Chuan1 (AUTHOR), Ferguson, Ian T.1 (AUTHOR), Klein, Benjamin1 (AUTHOR) bklein8@kennesaw.edu
Source: Journal of Electronic Materials. Jun2026, Vol. 55 Issue 6, p4951-4966. 16p.
Subjects: Raman spectroscopy, Metal organic chemical vapor deposition, Stress relaxation (Mechanics), Optical spectroscopy, Optical properties, Materials analysis, Heterostructures
Abstract: This paper presents an extensive structural and optical analysis of epitaxially grown n-type GaN thin films on Si (111) substrates by metal–organic chemical vapor deposition (MOCVD), both with and without atomic layer deposition (ALD) of an Al2O3 interlayer. A systematic investigation of four GaN/Si (111) heterostructures was conducted to assess the combined influence of GaN growth rate (1.25 µm h−1 and 1.8 µm h−1) and the incorporation of a ~20 nm Al2O3 interlayer on strain relaxation, phonon dynamics, and optical quality. The variable temperature-dependent (25–300°C) Raman spectroscopy technique showed clear E2 (high) and A1 (longitudinal optical [LO]) phonon behavior that was affected by biaxial stress, carrier concentration, and LO-phonon–plasmon coupling. The spatial correlation model confirmed increased phonon coherence and reduced intrinsic line width for samples containing the Al2O3 layer, signifying reduced defect density and enhanced crystalline uniformity. Complementary temperature-dependent spectroscopic ellipsometry measurements were performed to extract the refractive index, absorption coefficient, optical bandgap, and Urbach energy. The findings indicate a uniform redshift in the optical bandgap and a rise in Urbach energy with temperature, consistent with the Varshni and Urbach relations, respectively. The slower growth rate, along with Al2O3 interlayer, produced the lowest disorder and greatest optical stability. This study presents the combined effects of oxide-mediated strain relief and kinetic growth control, addressing a critical gap in the understanding of GaN-on-Si integration for cost-effective, high-performance optoelectronic and power devices. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:This paper presents an extensive structural and optical analysis of epitaxially grown n-type GaN thin films on Si (111) substrates by metal–organic chemical vapor deposition (MOCVD), both with and without atomic layer deposition (ALD) of an Al2O3 interlayer. A systematic investigation of four GaN/Si (111) heterostructures was conducted to assess the combined influence of GaN growth rate (1.25 µm h−1 and 1.8 µm h−1) and the incorporation of a ~20 nm Al2O3 interlayer on strain relaxation, phonon dynamics, and optical quality. The variable temperature-dependent (25–300°C) Raman spectroscopy technique showed clear E2 (high) and A1 (longitudinal optical [LO]) phonon behavior that was affected by biaxial stress, carrier concentration, and LO-phonon–plasmon coupling. The spatial correlation model confirmed increased phonon coherence and reduced intrinsic line width for samples containing the Al2O3 layer, signifying reduced defect density and enhanced crystalline uniformity. Complementary temperature-dependent spectroscopic ellipsometry measurements were performed to extract the refractive index, absorption coefficient, optical bandgap, and Urbach energy. The findings indicate a uniform redshift in the optical bandgap and a rise in Urbach energy with temperature, consistent with the Varshni and Urbach relations, respectively. The slower growth rate, along with Al2O3 interlayer, produced the lowest disorder and greatest optical stability. This study presents the combined effects of oxide-mediated strain relief and kinetic growth control, addressing a critical gap in the understanding of GaN-on-Si integration for cost-effective, high-performance optoelectronic and power devices. [ABSTRACT FROM AUTHOR]
ISSN:03615235
DOI:10.1007/s11664-026-12734-z