Bonding of Dissimilar Semiconductor Materials for Energy-Harvesting and Energy-Saving Devices
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-01-01 |
| Journal | Journal of the Vacuum Society of Japan |
| Authors | Naoteru Shigekawa |
| Institutions | Osaka City University |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Surface-Activated Bonding (SAB) for Advanced Hetero-Junction Devices
Section titled âTechnical Documentation & Analysis: Surface-Activated Bonding (SAB) for Advanced Hetero-Junction DevicesâExecutive Summary
Section titled âExecutive SummaryâThis documentation analyzes the research on Surface-Activated Bonding (SAB) of dissimilar semiconductors, focusing on applications in high-efficiency energy devices and the integration of diamond materials.
- Core Achievement: Successful fabrication of complex hetero-junctions (Si/SiC, InGaP/GaAs/Si, Diamond/Si) previously difficult or impossible via conventional crystal growth methods, utilizing the SAB technique.
- Diamond Integration: Single-Crystal Diamond (SCD) was successfully bonded to Si substrates at room temperature (RT) using Ar Fast Atom Beam (FAB) activation, paving the way for integrated diamond/Si power and sensing devices.
- Interface Control: Post-bonding thermal annealing (up to 1000 °C) was shown to recrystallize the amorphous interface layer (observed in Si/Si and Si/SiC junctions), significantly reducing interface state density and improving electrical characteristics (e.g., increasing Si/SiC activation energy from 0.33 eV to 1.02 eV).
- High-Efficiency Solar Cells: A triple-junction (3J) InGaP/GaAs/Si solar cell was fabricated using SAB, achieving a measured conversion efficiency of 25.5% under AM 1.5 G/one sun conditions.
- Low Interface Resistance: Achieving low series resistance is critical for high-efficiency devices. Interface resistance in highly doped (1019 cm-3) n+-GaAs/n+-Si junctions was reduced to 0.074 Ωcm2 after 400 °C annealing, meeting the requirements for non-concentrated photovoltaic applications.
- 6CCVD Value Proposition: 6CCVD provides the necessary ultra-high purity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates, along with custom polishing (Ra < 1 nm) and metalization services, essential for replicating and advancing this SAB research.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| SAB Chamber Pressure | < 1E-5 | Pa | Ultra-high vacuum required for surface activation |
| Ar FAB Acceleration Voltage | 1 - 2 | kV | Used for surface activation and native oxide removal |
| Bonding Load | 1 - 10 | MPa | Applied during room temperature bonding |
| Bonding Temperature | Room Temperature (RT) | °C | Key advantage of SAB over direct bonding |
| Post-Bonding Annealing (Si/Si) | 1000 | °C | 1 min in N2 ambient; promotes interface recrystallization |
| Interface State Density (Si/Si) | 2 x 1012 | cm-2eV-1 | Achieved after 1000 °C annealing (down from 1 x 1013) |
| Interface Resistance (n+-GaAs/n+-Si) | 0.074 | Ωcm2 | Achieved after 400 °C annealing (high doping 1019 cm-3) |
| Si/SiC Activation Energy (EA) | 1.02 | eV | After 1000 °C annealing (near Si bandgap 1.12 eV) |
| Si/SiC Activation Energy (EA) | 0.33 | eV | As-fabricated (dominated by trap-assisted tunneling) |
| 3J Solar Cell Efficiency (InGaP/GaAs/Si) | 25.5 | % | Measured under AM 1.5 G/one sun |
| 3J Solar Cell Short-Circuit Current (JSC) | 10.7 | mA/cm2 | Measured for the 5mm x 5mm cell |
| 3J Solar Cell Open-Circuit Voltage (VOC) | 2.92 | V | Measured for the 5mm x 5mm cell |
Key Methodologies
Section titled âKey MethodologiesâThe research relies heavily on the Surface-Activated Bonding (SAB) technique, followed by controlled thermal processing to optimize the hetero-junction interface.
- Surface Preparation: Substrates (Si, GaAs, SiC, Diamond) are placed in an ultra-high vacuum (UHV) chamber (achieving <1E-5 Pa).
- Surface Activation: The surfaces are irradiated using an Argon (Ar) Fast Atom Beam (FAB) with an acceleration voltage of 1-2 kV. This process removes native oxide layers, increases surface roughness (Ra), and activates the surface for bonding.
- Note on Diamond: Ar FAB irradiation causes partial graphitization (sp3 to sp2 conversion) on the diamond surface, which is hypothesized to facilitate room-temperature bonding to Si.
- Room Temperature Bonding: The activated substrates are brought into contact and bonded under an applied load of 1-10 MPa at room temperature (RT).
- Interface Evaluation: Cross-sectional Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) are used to confirm the interface structure, revealing a thin amorphous layer (several nm thick) in the as-fabricated junctions.
- Thermal Annealing: Post-bonding annealing (e.g., 1000 °C for 1 min in N2 ambient) is performed to induce recrystallization of the amorphous interface layer, reducing interface state density and improving macroscopic electrical properties (I-V characteristics).
- Electrical Characterization: Current-Voltage (I-V) characteristics are measured across the hetero-junctions (p-Si/p-Si, n-Si/n-Si, p+-Si/n-4H-SiC, etc.) at various temperatures to determine barrier height, interface state density, and activation energy.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced diamond materials and customization services required to replicate and extend the high-performance hetero-junction research demonstrated in this paper, particularly the integration of diamond with silicon.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the high-quality, integrated devices described (especially the Diamond/Si junction and high-voltage SiC devices), researchers require materials with exceptional purity, controlled doping, and superior surface finish.
| Research Requirement | 6CCVD Material Solution | Key Specification Match |
|---|---|---|
| Single-Crystal Diamond (SCD) | Optical Grade SCD or Electronic Grade SCD | Required for high-performance integrated Diamond/Si devices (Section 4.2). Available in thicknesses from 0.1 ”m to 500 ”m. |
| High-Voltage/High-Frequency Devices | High Purity SCD or Polycrystalline Diamond (PCD) | Diamondâs wide bandgap and high thermal conductivity are ideal for SiC/Si device heat spreading and integration. |
| High-Conductivity Interface Layers | Heavy Boron-Doped Diamond (BDD) | While the paper uses highly doped Si/GaAs, BDD can serve as a highly conductive, stable contact layer for future diamond-based SAB junctions. |
| Substrate Support | Custom Diamond Substrates | Available up to 10 mm thick for robust handling and integration of complex multi-layer stacks. |
Customization Potential
Section titled âCustomization PotentialâThe success of SAB relies on precise material dimensions, surface quality, and electrode placement. 6CCVD offers comprehensive customization services that directly address the needs of advanced bonding research:
- Custom Dimensions: The paper used 5mm x 5mm samples. 6CCVD provides custom laser cutting and sizing for both SCD and PCD plates/wafers up to 125mm (PCD), ensuring precise geometry for bonding experiments.
- Ultra-Low Surface Roughness: The paper highlights the importance of surface quality (Ra) for successful bonding. 6CCVD guarantees ultra-smooth polishing (Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD), minimizing interface voids and maximizing bond strength.
- Custom Metalization Schemes: The fabrication of the 3J solar cell and SiC diode required Ohmic electrodes (e.g., Ti/Pt/Au). 6CCVD offers in-house metalization capabilities including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to define custom electrode patterns directly onto the diamond or silicon substrates prior to bonding.
Engineering Support
Section titled âEngineering SupportâThe complexity of optimizing interface properties via SAB (balancing Ar FAB activation, doping concentration, and annealing temperature) requires deep material expertise.
- SAB Optimization: 6CCVDâs in-house PhD engineering team specializes in MPCVD growth and post-processing of diamond materials. We offer consultation on material selection, surface termination (e.g., hydrogen or oxygen termination), and polishing techniques optimized for Surface-Activated Bonding and similar wafer-bonding processes.
- Application Focus: We provide expert guidance for projects targeting integrated Diamond/Si devices and wide bandgap/narrow bandgap hetero structures (like Si/SiC), ensuring the diamond substrate properties (purity, doping, orientation) meet the specific electrical and thermal requirements of the final device.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value diamond materials directly to your research facility.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Research activities on surface activated bonding (SAB) of dissimilar semiconductor materials for targeting advanced energy-harvesting and energy-saving devices are reviewed.The structural and electrical properties of interfaces fabricated using the SAB technologies are examined.The change in the interface characteristics due to annealing after bonding is highlighted.The characteristics of SAB-based hybrid multi-junction solar cells, SiC/Si junctions as prototypes of wide bandgap/narrow bandgap hetero structures, and single-crystal diamond/Si junctions for integrating diamond and Si devices in the future are discussed.