Van der Waals β-Ga2O3 thin films on polycrystalline diamond substrates

At a Glance

Metadata	Details
Publication Date	2025-08-31
Journal	Nature Communications
Authors	Jing Ning, Zhichun Yang, Haidi Wu, X.-Y. Dong, Yaning Zhang
Institutions	Xidian University
Citations	1
Analysis	Full AI Review Included

Executive Summary

This study successfully demonstrates the epitaxial growth of highly oriented, single-crystalline Van der Waals beta-Gallium Oxide (VdW-β-Ga₂O₃) thin films on high-thermal-conductivity polycrystalline diamond substrates, overcoming major thermal management bottlenecks for next-generation power electronics.

Thermal Breakthrough: The use of a Graphene (2D material) interlayer enables VdW epitaxy, resulting in an ultralow Thermal Boundary Resistance (TBR_eff) of 2.82 m²K/GW. This value is one order of magnitude lower than previous bonding or interlayer approaches, fulfilling thermal requirements for kW-class power devices.
High Crystallinity: The 350 nm thick VdW-β-Ga₂O₃ films achieved exceptional crystal quality, exhibiting a minimum rocking curve Full Width at Half Maximum (FWHM) of 0.18° for the (201) orientation.
Scalable Growth Method: The films were grown using non-vacuum, cost-effective Mist Chemical Vapor Deposition (Mist-CVD), which is suitable for large-area deposition and uses affordable, safe precursors.
Lattice Mismatch Mitigation: Computational modeling confirmed that the Graphene interlayer significantly enhances adsorption energy and reduces the lattice mismatch coefficient between β-Ga₂O₃ (201) and Graphene to a structurally stable 4.9%.
High-Performance Device: Photodetectors fabricated using the VdW-β-Ga₂O₃ film demonstrated superior performance metrics, including a Photo-to-Dark Current Ratio (PDCR) of 10⁶ and a high responsivity of 210 A/W.
Stress Management: In-situ Raman measurements confirmed that the Graphene interlayer effectively alleviates interfacial thermal expansion stress between the Ga₂O₃ film and the diamond substrate.

Technical Specifications

Parameter	Value	Unit	Context
Thermal Boundary Resistance (TBR_eff)	2.82	m²K/GW	β-Ga₂O₃/Diamond interface (Sample 2, bare diamond)
Thermal Conductivity (TC)	7.19	W/mK	350 nm thick VdW-β-Ga₂O₃ film
Rocking Curve FWHM (201)	0.18	°	Smallest value achieved at 760 °C growth temperature
RMS Roughness	6.71	nm	350 nm thick film, grown at 760 °C
Film Thickness	350	nm	Optimized thickness for minimum FWHM
Lattice Mismatch (β-Ga₂O₃ [201] vs Graphene)	4.9	%	Calculated coefficient, ensuring structural stability (threshold is 6%)
Photo-to-Dark Current Ratio (PDCR)	10⁶	N/A	Fabricated photodetector performance
Responsivity (R)	210	A/W	Fabricated photodetector performance
Rise Time (t₁)	54	ms	Photodetector response time
Decay Time (t₂)	4	ms	Photodetector response time
Diamond Substrate TC (300 K)	greater than 1800	W/mK	Polycrystalline diamond (Element Six TM180) specification
Oxygen Vacancy Density	15.1	%	Lowest ratio (O_II/(O_I + O_II)) achieved at 1000 sccm O₂ flow

Key Methodologies

The VdW-β-Ga₂O₃ films were grown using Mist Chemical Vapor Deposition (Mist-CVD) on polycrystalline diamond substrates pre-treated with a Graphene interlayer.

Graphene Preparation and Transfer:
- Monolayer Graphene (ML) was grown on 25-µm-thick Alfa Aesar copper foil via CVD (40 sccm CH₄, 40 sccm H₂, followed by 10 sccm CH₄, 20 sccm H₂).
- The ML Graphene was transferred onto Element Six TM180 polycrystalline diamond substrates using a Methyl Methacrylate (MMA) support layer and ammonium persulfate etching.
- The diamond substrate was cleaned with acetone, alcohol, deionized water, and dilute HF solution to ensure an atomically clean interface prior to transfer.
Mist-CVD Epitaxial Growth (Optimized Recipe):
- Precursor: Gallium acetylacetonate (C₁₅H₂₁O₆Ga) dissolved in deionized water and concentrated hydrochloric acid (HCl).
- Substrate Temperature: Optimized at 760 °C (range 700-800 °C) under an Argon (Ar) atmosphere.
- Atomization: An ultrasonic nebulizer (1.7 MHz) converted the precursor solution into small droplets.
- Carrier Gas (O₂): Optimized flow rate of 600 sccm (range 300-1000 sccm) to control oxygen partial pressure and minimize oxygen vacancies.
- Diluting Gas (Ar): Flow rate maintained at 3000 sccm.
- Growth Duration: 30-40 minutes.
Characterization Techniques:
- Atomic Structure: Transmission Electron Microscopy (TEM) and High-Resolution TEM (HR-TEM) confirmed the VdW interface and crystal orientations ((201) predominant).
- Crystallinity: X-ray Diffraction (XRD) and rocking curve measurements determined crystal orientation and FWHM.
- Surface Morphology: Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) measured RMS roughness and grain coalescence.
- Stress and Thermal Properties: In-situ temperature-dependent Raman spectroscopy measured thermal expansion stress release. Time-Domain Thermoreflectance (TDTR) measured thermal conductivity and TBR_eff.

Commercial Applications

The successful integration of high-crystallinity β-Ga₂O₃ with diamond via VdW epitaxy and Mist-CVD addresses critical thermal limitations, enabling the development of next-generation devices in several high-power and high-frequency sectors.

High-Power Electronics:
- Ultra-High Voltage MOSFETs and Schottky Diodes (β-Ga₂O₃ has a Baliga’s Figure of Merit 4 times better than GaN).
- kW-class power devices requiring superior thermal management to prevent performance degradation due to self-heating effects.
- High-efficiency power converters and inverters for electric vehicles and smart grids.
Ultraviolet (UV) Optoelectronics:
- Solar-blind photodetectors (PDs) utilizing the high PDCR (10⁶) and responsivity (210 A/W) of the VdW-β-Ga₂O₃ films.
- UV sensors for flame detection, space communication, and environmental monitoring.
Advanced Substrate Technology:
- Development of wafer-scale Ga₂O₃/Diamond composite substrates for thermal dissipation in high-density electronic packaging.
- Heterogeneous integration platforms where lattice mismatch is traditionally prohibitive.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-025-63666-x