Thermal diffusion boron doping of single-crystal natural diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-05-24 |
| Journal | Journal of Applied Physics |
| Authors | JungâHun Seo, Henry Wu, Solomon Mikael, Hongyi Mi, James P. Blanchard |
| Institutions | University of WisconsinâMadison, Wisconsin Institutes for Discovery |
| Citations | 40 |
| Analysis | Full AI Review Included |
Thermal Diffusion Boron Doping of Single-Crystal Diamond: Technical Analysis and 6CCVD Solutions
Section titled âThermal Diffusion Boron Doping of Single-Crystal Diamond: Technical Analysis and 6CCVD SolutionsâThis document analyzes the technical requirements and outcomes of the research regarding the thermal diffusion boron doping of Single-Crystal Diamond (SCD) and outlines how 6CCVDâs expert manufacturing capabilities directly support the replication and scaling of this advanced wide bandgap technology.
Executive Summary
Section titled âExecutive SummaryâThe research presents a novel, highly effective thermal diffusion method for achieving substitutional boron doping in SCD, bypassing the critical limitations of conventional techniques (ion implantation and in-situ doping).
- Advanced Doping Mechanism: Substitutional p-type doping (Boron) is achieved via thermal diffusion using heavily doped Silicon Nanomembranes (SiNMs) bonded to the SCD surface.
- Lattice Damage Mitigation: Unlike ion implantation, this method prevents lattice damage and avoids graphitization transitions on the diamond surface, maintaining high crystal quality (FWHM of Raman peak < 5 cm-1).
- Low-Temperature Processing: Effective doping is achieved at a relatively low Rapid Thermal Annealing (RTA) temperature (800 °C), significantly below the typical 1450 °C required for post-implantation activation and damage repair.
- Enhanced Diffusion: The intimate SiNM-diamond interface facilitates a vacancy exchange mechanism, dramatically lowering the energy barrier required for boron transport into the diamond lattice.
- High-Performance Device Demonstration: The selectively doped SCD was used to fabricate vertical p-i diodes, demonstrating the highest reported breakdown voltage (~800 V) for a non-in-situ doped diamond diode.
- Critical Application Path: This technique establishes a viable, scalable path for using SCD in high-voltage power conversion systems and radio-frequency electronics.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Natural SCD (nSCD), Type-IIa | N/A | High-quality base material for doping. |
| Substrate Dimensions | 2 x 2 | mm2 | Diode fabrication size. |
| Substrate Thickness | 120 | ”m | Bulk thickness of nSCD plate. |
| RTA Annealing Temperature | 800 | °C | Thermal diffusion temperature. |
| RTA Annealing Time | 40 | min | Duration under Nitrogen (N2) ambient. |
| Boron Surface Concentration | ~1 x 1019 | cm-3 | Measured by SIMS/C-V. Comparable to ion implantation. |
| Boron Doping Depth | ~70 | nm | Shallow p-type layer formation. |
| Effective Diffusivity (D) | 2 x 10-16 | cm2/s | Near SiNM interface at 800 °C. Three orders magnitude higher than conventional. |
| Boron Activation Energy (EA) | 0.283 | eV | Extracted via Arrhenius fit (J0 α T5/2 exp(-EA/kT)). |
| Diode Breakdown Voltage (Vbr) | ~800 | V | Highest reported for non-in-situ doped diamond diode. |
| Diode Ideality Factor | 1.3 | N/A | Indicates good rectifying behavior. |
| Forward Current Density | 0.07 | A/cm2 | Measured at +5 V bias. |
| Initial SCD Surface Roughness (Rq) | 0.35 to 1.05 | nm | Measured by AFM (parallel and perpendicular to polishing grooves). |
Key Methodologies
Section titled âKey MethodologiesâThe core process relies on preparing a heavily boron-doped Si Nanomembrane (SiNM) and deterministically transferring it onto the nSCD substrate prior to RTA.
- SiNM Preparation (Boron Doping):
- Starting Material: SOI wafer (200 nm top Si layer, 145 nm buried oxide).
- Screen Oxide: 30 nm of thermally grown SiO2 applied.
- Ion Implantation: Boron ions at 16 KeV, 3 x 1015 atoms/cm2 dose, 7° incident angle.
- Annealing: Furnace anneal at 950 °C for 90 min under N2 ambient (for Si recrystallization and dopant redistribution, achieving 1020 cm-3 at bottom Si layer).
- SiNM Release and Surface Preparation:
- SiNM Release: Selective etching of the buried oxide (BOX) using concentrated 49% Hydrofluoric Acid (HF).
- Diamond Cleaning: nSCD plates cleaned in ammonium sulphuric acid solution (30 min at 200 °C), followed by ammonia hydroxide/hydrogen peroxide solution rinse (DI water rinse) to achieve contaminant-free, native oxide-free surface.
- Transfer and Diffusion:
- Transfer Printing: Released SiNMs deterministically transferred onto nSCD plates using stamp-assisted transfer printing.
- Thermal Diffusion: RTA anneal at 800 °C for 40 minutes under N2 ambient.
- Device Fabrication (p-i Diode):
- Cathode Metalization (Bottom): Ti/Pt/Au (20/50/100 nm) deposited by e-beam evaporation.
- Ohmic Annealing: RTA at 450 °C.
- Anode Metalization (Top): Ti/Au (20 nm/150 nm) formed on top of the SiNM.
- Selective Etching: Anode metal pads used as a mask to dry etch SiNM and subsequently etch the diamond surface 50 nm down (using RIE with O2) to define the active device area and minimize surface current flow.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research validates a crucial technique for creating high-performance diamond electronic devices. 6CCVD is uniquely positioned to supply the high-quality SCD materials, advanced substrates, and custom processing required to industrialize or extend this research.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or advance this p-type thermal diffusion process, 6CCVD recommends the following high-purity MPCVD Diamond materials:
| 6CCVD Product Line | Recommendation Basis | Relevance to Research |
|---|---|---|
| Electronic Grade Single Crystal Diamond (SCD) | Low-defect, Type-IIa equivalent material, superior to natural diamond (nSCD) used in study. | Required for high-voltage devices (up to 107 V/cm breakdown potential). CVD SCD was confirmed compatible by the authors. |
| Custom SCD Substrates (120 ”m to 500 ”m) | Precise thickness control is required for target breakdown voltage (Vbr). | Paper used 120 ”m thick plates; 6CCVD provides custom thickness control for optimized depletion/blocking layers. |
| Low-Defect Polycrystalline Diamond (PCD) | For non-epitaxial, large-area applications (up to 125mm). | While the paper focused on SCD, the low-temperature, damage-free doping method is highly relevant for large-area PCD electronics where crystal quality is paramount. |
Customization Potential
Section titled âCustomization PotentialâThe successful implementation of this thermal diffusion technique relies on precise mechanical preparation and highly controlled metal contactsâboth core capabilities of 6CCVD.
| Service | 6CCVD Capability | Direct Link to Research Need |
|---|---|---|
| Custom Dimensions | Plates and wafers available up to 125mm (PCD). Laser cutting services for precise dimensions (e.g., the 2 x 2 mm2 diodes). | Enables device scaling and production of application-specific geometries beyond standard plates. |
| High-Fidelity Polishing | Guaranteed Ra < 1 nm (SCD) and Ra < 5 nm (PCD, inch-size). | Crucial for the SiNM transfer printing process, which relies on intimate contact (the paper noted Rq down to 0.35 nm). 6CCVD meets or exceeds this required surface quality. |
| Integrated Metalization | Full internal capability for deposition of Au, Pt, Pd, Ti, W, Cu layers. | The paper used Ti/Pt/Au (20/50/100 nm) stacks. 6CCVD can replicate or customize these multilayer ohmic contact schemes directly onto the SCD surface or SiNM. |
Engineering Support
Section titled âEngineering SupportâThe enhanced boron diffusion mechanism (vacancy exchange facilitated by Si-C bonding) suggests that optimizing the interface between the SiNM and SCD is key. 6CCVDâs in-house PhD team offers consultation services focusing on material preparation for similar high-voltage power rectification and switching projects.
- Defect Engineering: Our experts can assist in specifying SCD growth recipes to manage native vacancy concentrations, potentially improving the efficiency and consistency of the SiNM-based thermal diffusion doping process.
- Surface Preparation Optimization: Consultation on specialized surface cleaning and termination techniques to maximize the bonding quality necessary for the vacancy-exchange mechanism.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occurs at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.