Orientation-dependent electric transport and band filling in hole co-doped epitaxial diamond films
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-06-08 |
| Journal | Applied Surface Science |
| Authors | Erik Piatti, A. Pasquarelli, R. S. Gonnelli |
| Institutions | UniversitÀt Ulm, Polytechnic University of Turin |
| Citations | 11 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Orientation-Dependent Hole Co-Doping in Epitaxial Diamond
Section titled âTechnical Documentation & Analysis: Orientation-Dependent Hole Co-Doping in Epitaxial DiamondâThis document analyzes the research detailing orientation-dependent electric transport in hole co-doped epitaxial diamond films, focusing on the combination of ionic gating and Boron substitution. The findings are leveraged to showcase 6CCVDâs superior material science capabilities for advanced quantum and electronic device engineering.
Executive Summary
Section titled âExecutive Summaryâ- Novel Co-Doping Approach: The research successfully demonstrates a co-doping technique combining ionic gating (Electric Double Layer Transistors, EDLTs) and Boron (B) substitution to tune free hole density in H-terminated epitaxial diamond films.
- Strong Orientation Dependence: Electric transport properties, particularly gate capacitance (C$_{G}$) and mobility ($\mu$), show extreme sensitivity to crystal orientation, comparing (111) and (110) facets.
- Capacitance Enhancement: B-doping led to a five-fold increase in C$_{G}$ in the (110)-oriented films (up to 2.53 ”F cm-2), linking directly to the energy-dependence of the electronic density of states (DOS).
- Mobility Suppression: While B-doping increased intrinsic hole density (up to 1.5 $\cdot$ 1014 h+cm-2), it significantly suppressed mobility, particularly in the (111) orientation ($\mu$ dropped to $\approx 3$ cm2V-1s-1).
- Metallicity Frustration: The co-doping approach resulted in a frustrated insulator-to-metal transition (IMT) in the (110) surface and a re-entrant IMT in the (111) surface, falling short of the required carrier density (6 $\cdot$ 1014 h+cm-2) for predicted high-Tc superconductivity.
- Material Requirement: Achieving robust metallicity and high-Tc superconductivity requires optimizing crystal growth to minimize disorder and precisely control ultra-thin B-doped layer thickness (nominal 2 nm used).
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the gate-dependent transport measurements and DFT calculations:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Temperature (T) | $\approx 240$ | K | Optimal EDLT operation (above PES glass transition) |
| Maximum Total Carrier Density (n2D) | $\lt 2.1 \cdot 10^{14}$ | h+cm-2 | Achieved maximum (Target for SC is $6 \cdot 10^{14}$ h+cm-2$) | |
| | Intrinsic Hole Density (n0) | $1.5 \pm 0.4 \cdot 10^{14}$ | h+cm-2 | Highest value (B-doped (111) surface) | ||
| H-Terminated C$_{G}$ (111) | $1.36 \pm 0.41$ | ”F cm-2 | Gate Capacitance (H-terminated) |
| H-Terminated C$_{G}$ (110) | $0.44 \pm 0.13$ | ”F cm-2 | Gate Capacitance (H-terminated) |
| B-Doped C$_{G}$ (111) | $2.06 \pm 0.62$ | ”F cm-2 | Gate Capacitance (B-doped) |
| B-Doped C$_{G}$ (110) | $2.53 \pm 0.76$ | ”F cm-2 | Gate Capacitance (B-doped) |
| H-Terminated Mobility ($\mu$) | $53 \div 145$ | cm2V-1s-1 | Range across (111) and (110) surfaces |
| B-Doped Mobility ($\mu$) | $1.9 \div 3.3$ | cm2V-1s-1 | Lowest range (B-doped (111) surface) |
| Epitaxial Buffer Layer Thickness | $100$ | nm | Undoped intrinsic layer |
| B-Doped Layer Thickness | $2$ | nm | Nominal thickness of the active layer |
| CVD Reactor Pressure | $2$ | kPa | MPCVD growth parameter |
| CVD Reactor Temperature | $750$ | °C | MPCVD growth parameter |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure combined advanced MPCVD growth with ionic gating techniques (EDLT architecture) and ab initio Density Functional Theory (DFT) calculations.
- Substrate Preparation: Commercial Ib-type single crystal diamond substrates ((111) and (110) orientation) were thoroughly cleaned using a multi-step chemical process (Acetone, Isopropanol, Chromosulphuric acid, HCl:H2O2, H2O2:NH4OH, HCl:HNO3, H2SO4:H2O2).
- Epitaxial Growth (MPCVD):
- A nominally undoped, 100 nm thick intrinsic buffer layer was grown first.
- An additional 2 nm thick B-doped layer was subsequently grown on half the samples.
- Parameters: Pressure 2 kPa, Reactor Temperature 750°C, Plasma RF Power 750 W, H2 flow 200 sccm, varying CH4 concentration. Boron supplied via a solid B-coated wire.
- Surface Termination: Growth was performed in H2/CH4 atmosphere, resulting in H-termination of the diamond surfaces.
- Device Fabrication (EDLT):
- Four-wire electrical contacts (source, drain, longitudinal voltage probes) were realized using silver conductive paste.
- A side gate (thin gold leaf) and a reference electrode (thin gold wire) were incorporated.
- The Polymer-Electrolyte System (PES) was drop-casted and UV-cured (BEMA and EMIM-TFSI ionic liquid).
- Transport Measurement: Gate-dependent electric transport measurements were performed at $T \approx 240$ K.
- Sheet conductance ($\sigma_{2D}$) was measured via four-wire resistance.
- Gate-induced hole density ($\Delta n_{2D}$) and gate capacitance (C$_{G}$) were determined using Double-Step Chronocoulometry (DSCC).
- Theoretical Modeling: Ab initio DFT calculations (using the Jellium model) were performed to determine the electronic band structure and Density of States (DOS) for H-terminated, hole-doped (111) and (110) slabs.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the critical need for ultra-precise material controlâspecifically, crystal orientation, doping concentration, and layer thicknessâto manipulate quantum capacitance and carrier mobility in diamond EDLTs. 6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials necessary to replicate, optimize, and extend this research toward achieving robust metallicity and high-temperature superconductivity.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Solution | Material Specification |
|---|---|---|
| Substrate & Buffer Layer | Optical Grade SCD | High-purity, low-disorder Single Crystal Diamond (SCD) wafers. Essential for minimizing extrinsic disorder noted in the paper. |
| Active Doping Layer | Precisely Doped SCD (BDD) | Ultra-thin, highly controlled Boron-Doped Diamond (BDD) epitaxial layers. Required for achieving high intrinsic hole density ($n_0$) without excessive lattice disorder. |
| Crystal Orientation | Custom Oriented SCD Wafers | SCD wafers available in standard (100), (111), and custom (110) orientations up to inch size, critical for exploiting orientation-dependent DOS effects. |
| Surface Quality | SCD Polishing | Polishing to achieve surface roughness Ra < 1 nm, significantly improving upon the $S_q \approx 2.4$ nm to $3.8$ nm reported in the paper, thereby reducing discontinuities in the conducting surface layer. |
Customization Potential
Section titled âCustomization PotentialâThe paper emphasizes that optimizing the crystal growth and B doping process is necessary to avoid discontinuities and minimize mobility degradation. 6CCVD offers bespoke engineering services to address these challenges:
- Ultra-Precise Thickness Control: 6CCVD guarantees SCD layer thickness control from 0.1 ”m up to 500 ”m. We can reliably produce the required 100 nm buffer layer and the critical 2 nm B-doped active layer with superior uniformity and repeatability.
- Custom Doping Profiles (BDD): We offer tailored Boron doping concentrations (BDD) to fine-tune the intrinsic hole density ($n_0$) and optimize the quantum capacitance, crucial for overcoming the IMT frustration observed in this study.
- Advanced Metalization Services: The EDLT architecture requires precise electrical contacts (Au gate, Ag paste contacts). 6CCVD provides in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to integrate robust, high-quality contacts directly onto the diamond surface.
- Large Area PCD: While this study focused on SCD, 6CCVD offers Polycrystalline Diamond (PCD) plates up to 125 mm diameter with polishing down to Ra < 5 nm, suitable for scaling up EDLT or other field-effect device architectures.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and CVD experts can provide comprehensive engineering support for projects targeting High-Density 2D Hole Gas (2DHG) and Field-Induced Superconductivity in diamond. We assist clients in selecting the optimal substrate orientation, doping concentration, and layer stack design to maximize carrier density and mobility simultaneously, addressing the trade-offs identified in this research.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2004 - Superconductivity in diamond [Crossref]
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- 2007 - Observation of a superconducting gap in boron-doped diamond by laser-excited photoemission spectroscopy [Crossref]
- 2008 - Superconducting diamond: an introduction [Crossref]
- 2015 - Signature of high Tc above 25 K in high quality superconducting diamond [Crossref]
- 2004 - Three-dimensional MgB2-type superconductivity in hole-doped diamond [Crossref]
- 2004 - Superconductivity in boron-doped diamond [Crossref]