Electrical and thermal characterisation of liquid metal thin-film Ga$$_2$$O$$_3$$–SiO$$_2$$ heterostructures
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-03-01 |
| Journal | Scientific Reports |
| Authors | Alexander Petkov, Abhishek Mishra, Mattia Cattelan, D. Field, James W. Pomeroy |
| Institutions | University of Bristol |
| Citations | 7 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Ga${2}$O${3}$-Diamond Heterostructures
Section titled “Technical Documentation & Analysis: Ga${2}$O${3}$-Diamond Heterostructures”Executive Summary
Section titled “Executive Summary”This research investigates the electrical and thermal properties of thin-film Ga${2}$O${3}$ heterostructures, confirming that Gallium Oxide’s inherently low thermal conductivity (k $\approx$ 11-27 W/mK) necessitates integration with ultra-high thermal conductivity materials for high-power device applications.
- Thermal Challenge: The out-of-plane thermal conductivity of the thin-film Ga${2}$O${3}$ was measured at $3 \pm 0.5$ W/mK, highlighting the critical need for a high-k substrate to manage heat dissipation.
- Diamond as the Solution: The paper explicitly cites modeling showing that a Ga${2}$O${3}$-Diamond superjunction would lead to an approximately 60% reduction in temperature rise compared to standard Ga${2}$O${3}$ devices.
- Favorable Band Alignment: High-resolution XPS data was used to predict the valence band offset (VBO) of Ga${2}$O${3}$ relative to diamond at -2.3 eV, resulting in a large conduction band offset (CBO) of -2.85 eV.
- High-Voltage Potential: This predicted Type II band alignment creates significant energetic barriers for minority carriers, supporting the design of high-breakdown-field devices, such as Ga${2}$O${3}$-Al${2}$O${3}$-Diamond Schottky barrier diodes.
- 6CCVD Value Proposition: 6CCVD provides the necessary Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates, offering thermal conductivities up to 2000 W/mK, custom dimensions up to 125mm, and precise metalization required to realize these next-generation Ga${2}$O${3}$-Diamond power devices.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the electrical and thermal characterization of the Ga${2}$O${3}$-SiO${2}$ heterostructures, including key predictions for the Ga${2}$O$_{3}$-Diamond interface.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Ga${2}$O${3}$ Film Thickness Range | 8 to 30 | nm | Deposited via liquid metal exfoliation |
| Out-of-Plane Thermal Conductivity (k) | 3 $\pm$ 0.5 | W/mK | Thin-film Ga${2}$O${3}$ (30 nm thickness) |
| Predicted Valence Band Offset (VBO) | -2.3 | eV | Ga${2}$O${3}$ relative to Diamond |
| Predicted Conduction Band Offset (CBO) | -2.85 | eV | Ga${2}$O${3}$ relative to Diamond |
| Measured Valence Band Offset (VBO) | 0.1 | eV | Ga${2}$O${3}$ relative to SiO$_{2}$ |
| Ga${2}$O${3}$ Band Gap (Assumed) | 4.9 | eV | Used for CBO calculation |
| Annealing Temperature | 250 | °C | Post-deposition stabilization (1 hour in O$_{2}$) |
| Cr Transducer Thickness (TTR) | 10 | nm | Used for Transient Thermoreflectance |
| Au Transducer Thickness (TTR) | 100 | nm | Used for Transient Thermoreflectance |
| Si Substrate Thickness | 400 | µm | Used in TTR measurement stack |
Key Methodologies
Section titled “Key Methodologies”The experiment utilized advanced thin-film deposition and characterization techniques to determine the interfacial properties of the Ga${2}$O${3}$ heterostructures.
- Deposition: Thin-film Ga${2}$O${3}$ was deposited onto a thermally oxidized Si substrate using liquid gallium layer delamination (exfoliation method).
- Stabilization: Samples were annealed in oxygen at 250 °C for 1 hour to stabilize the stoichiometry of the deposited Ga${2}$O${3}$ film.
- Thickness Verification: Atomic Force Microscopy (AFM) was used in tapping mode to confirm film thicknesses ranging from 8 nm to 30 nm.
- Electrical Characterization: High resolution X-ray Photoelectron Spectroscopy (XPS) was employed using a monochromatic Al K$\alpha$ excitation source (hv = 1486.7 eV) to measure core levels and valence band maxima, enabling the calculation of band offsets.
- Thermal Characterization (TTR): Transient Thermoreflectance (TTR) was used to measure the out-of-plane thermal conductivity.
- A 10 nm Chromium (Cr) adhesion layer and 100 nm Gold (Au) transducer layer were thermally evaporated onto the surface prior to TTR measurement.
- A 355 nm Nd:YAG pump laser (10 ns pulse) and a 532 nm probe laser were used for heating and reflectivity measurement, respectively.
- Thermal Modeling: An analytical model and 2D Finite Element Method (FEM) simulation were used to fit the TTR data and model the steady-state temperature rise across the heterojunction.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research confirms that diamond is the superior material for thermal management and high-voltage integration with Ga${2}$O${3}$. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond materials and customization services required to advance Ga${2}$O${3}$-on-Diamond technology.
| Research Requirement/Challenge | 6CCVD Solution & Capability | Applicable Material Specification |
|---|---|---|
| Ultra-High Thermal Management (Required k $\approx$ 1000-2000 W/mK) | SCD and PCD substrates optimized for thermal spreading in high-power devices (e.g., Ga${2}$O${3}$ MOSFETs). | Thermal Grade SCD/PCD (Substrates up to 10mm thick). |
| Large-Area Heterostructure Integration | Custom dimensions and large-area wafers suitable for industrial wafer bonding or direct deposition. | PCD Wafers up to 125mm diameter. |
| Minimizing Thermal Boundary Resistance (TBR) | High-quality surface preparation is essential for low-TBR interfaces (e.g., wafer bonding). | Polishing: Ra < 1nm (SCD) or Ra < 5nm (Inch-size PCD). |
| Custom Transducer/Electrode Layers (Paper used Cr/Au for TTR) | In-house metalization capability for precise, multi-layer stacks required for TTR, XPS, or device electrodes. | Metalization: Au, Pt, Pd, Ti, W, Cu (Custom stack deposition). |
| P-Type Layer for Superjunctions (Addressing the lack of p-type Ga${2}$O${3}$) | Boron-Doped Diamond (BDD) provides a stable, high-quality p-type layer for Ga${2}$O${3}$ heterojunctions. | Boron-Doped Diamond (BDD) (Custom doping levels available). |
Applicable Materials
Section titled “Applicable Materials”To replicate or extend this research into high-performance Ga${2}$O${3}$-Diamond devices, 6CCVD recommends the following materials:
- Optical Grade SCD: Ideal for high-purity, low-defect substrates necessary for subsequent epitaxial growth of Ga${2}$O${3}$ or Al${2}$O${3}$ buffer layers, ensuring optimal electronic performance.
- Thermal Grade PCD: Provides cost-effective, large-area thermal spreading for commercial applications where wafer size (up to 125mm) is critical.
- Heavy Boron Doped PCD/SCD: Required for the p-type component in the proposed Ga${2}$O${3}$-Diamond superjunctions, leveraging diamond’s superior hole mobility.
Customization Potential
Section titled “Customization Potential”The TTR measurements relied on specific 10 nm Cr / 100 nm Au transducer layers. 6CCVD offers precise, internal metalization services to deposit these and other complex stacks (e.g., Ti/Pt/Au) directly onto diamond substrates, ensuring compatibility with subsequent Ga${2}$O${3}$ processing. We also offer custom laser cutting for unique device geometries.
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team are experts in wide bandgap semiconductor integration and thermal management. We can assist researchers and engineers in optimizing diamond material selection, surface termination, and interface preparation to achieve the lowest possible thermal boundary resistance and maximize the performance benefits of the predicted Ga${2}$O${3}$-Diamond band alignment.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.