The Undoped Polycrystalline Diamond Film—Electrical Transport Properties
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-09-12 |
| Journal | Sensors |
| Authors | Szymon Łoś, K. Fabisiak, K. Paprocki, Mirosław Szybowicz, Anna Dychalska |
| Institutions | Bydgoszcz University of Science and Technology, Institute of Mathematics |
| Citations | 10 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Electrical Transport in Polycrystalline Diamond
Section titled “Technical Documentation & Analysis: Electrical Transport in Polycrystalline Diamond”This document analyzes the research paper, “The Undoped Polycrystalline Diamond Film—Electrical Transport Properties,” to extract critical technical data and align the findings with 6CCVD’s advanced MPCVD diamond manufacturing capabilities, focusing on driving sales for high-performance electronic and sensing applications.
Executive Summary
Section titled “Executive Summary”The research successfully demonstrates that the electrical transport properties of undoped polycrystalline diamond (PCD) films are critically dependent on the level of surface hydrogenation achieved during Hot Filament Chemical Vapor Deposition (HF CVD).
- Key Control Parameter: The degree of surface hydrogenation (H concentration) was shown to be the primary mechanism for tuning electrical conductivity and defect density.
- Performance Correlation: Higher hydrogenation levels (up to 26 at.%) correlate directly with increased surface conductivity, lower activation energies (down to 56 meV), and significantly reduced grain boundary potential barriers ($\Phi_{GB}$ down to 60 meV).
- Conduction Mechanisms: Two distinct transport regimes were confirmed: thermally activated band conduction (200-300 K) and Mott Variable Range Hopping (M-VRH) (< 200 K), crucial for low-temperature device modeling.
- Defect Density Control: By varying growth pressure, the Density of Localized States near the Fermi level N(EF) was tuned across a range of 9.2 x 1013 to 4.7 x 1014 eV-1cm-3.
- Structural Impact: Increasing growth pressure reduced average grain size (66 nm down to 35 nm) and decreased hydrogenation, leading to higher resistivity films.
- Commercial Relevance: These findings confirm the necessity of precise surface engineering and material quality control for developing reliable diamond-based microelectronic devices and high-sensitivity sensors.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the analysis of the three polycrystalline diamond films (DF40, DF60, DF80).
| Parameter | Value Range | Unit | Context |
|---|---|---|---|
| Film Thickness | 3-4 | µm | Polycrystalline Diamond (PCD) |
| Substrate Material | n-type single crystalline Si | N/A | Used for hetero-junction growth |
| Substrate Temperature | 1100 | K | Estimated growth temperature |
| Filament Temperature | 2300 | K | Tungsten filament temperature (HF CVD) |
| Gas Composition | 3 vol% CH4 in H2 | N/A | Carbon source and hydrogen-rich plasma |
| H Concentration (DF40 to DF80) | 26 ± 1 to 17 ± 1 | at.% | Decreases with increasing pressure |
| Average Grain Size (L) | 66 ± 1 to 35 ± 1 | nm | Decreases with increasing pressure |
| Activation Energy (Ea) | 56 to 228 | meV | Measured in the 200-300 K band conduction regime |
| Grain Boundary Barrier ($\Phi_{GB}$) | 60 to 257 | meV | Increases as hydrogenation decreases |
| Density of States N(EF) | 9.2 x 1013 to 4.7 x 1014 | eV-1cm-3 | Calculated using the Mott VRH model |
| Hopping Energy (W) | 32 to 57 | meV | Increases as hydrogenation decreases |
| Hopping Distance (R) | 4.2 x 10-4 to 1.23 x 10-5 | cm | Decreases as hydrogenation decreases |
| Raman Diamond Peak | 1331.6 to 1331.9 | cm-1 | Characteristic diamond structure peak |
| Conductivity Measurement Range | 90-300 | K | Temperature range for I-V-T measurements |
Key Methodologies
Section titled “Key Methodologies”The experiment focused on synthesizing and characterizing undoped polycrystalline diamond films grown under controlled pressure variations.
-
Synthesis (HF CVD):
- Polycrystalline diamond films were grown on (100) oriented n-Si wafers using Hot Filament CVD.
- The carbon source was methane (3 vol%) diluted in hydrogen (H2).
- The total gas flow rate was fixed at 100 sccm.
- Three different working gas pressures were tested: 40, 60, and 80 hPa.
- Substrates were mechanically polished with 1 µm diamond powder prior to growth to enhance nucleation.
- The tungsten filament was heated to 2300 K; the substrate temperature was estimated at 1100 K.
-
Structural Characterization:
- SEM: Used to determine film thickness (3-4 µm) and microcrystal grain size (2 µm down to < 1 µm).
- XRD (DRON-4a): Used to confirm diamond reflections (111, 220, 331) and calculate average grain sizes (L) using the Debye-Scherrer formula.
- Raman Spectroscopy (Renishaw inVia): Used to assess film quality, phase composition (diamond vs. sp2 amorphous carbon), and estimate hydrogen concentration (H [at.%]) based on the G-band intensity and photoluminescence background slope.
-
Electrical Measurement (I-V-T):
- Electrode Preparation: Diamond surfaces and substrates were metalized by gold (Au) evaporation to create four-probe electrode contacts in a hetero-junction configuration (n-Si/p-diamond).
- Setup: Measurements were performed in an Oxford Optistat cryostat under vacuum (77-300 K).
- Instrumentation: Rigol DG1022A (voltage source, 4-20 V peak-to-peak), Keithley 6485 picoammeter (current registration), Fluke 8505A (potential drop).
- Analysis: Conductivity ($\sigma$) versus inverse temperature (1/T) plots were analyzed to determine activation energy (Ea) in the high-temperature regime and to apply the Mott Variable Range Hopping (M-VRH) model below 200 K to calculate N(EF), R, and W.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”This research underscores the critical role of material quality, surface termination, and defect control in achieving predictable electrical transport in diamond films—requirements perfectly matched by 6CCVD’s advanced MPCVD capabilities.
Applicable Materials for Replication and Optimization
Section titled “Applicable Materials for Replication and Optimization”To replicate and extend this research into commercial devices (e.g., high-temperature electronics or gas sensors), 6CCVD recommends the following materials:
- Polycrystalline Diamond (PCD) Wafers: 6CCVD provides high-purity, undoped PCD films, ideal for applications where surface conductivity is induced via hydrogenation. We offer precise control over grain size and sp2 content, allowing researchers to systematically tune the grain boundary barrier ($\Phi_{GB}$) and N(EF) as demonstrated in the paper.
- Single Crystal Diamond (SCD) Substrates: For applications requiring the highest mobility and minimal grain boundary effects, 6CCVD offers high-quality SCD films (0.1 µm to 500 µm thick) that can be surface-terminated (H-terminated) to achieve superior p-type surface conductivity without the structural complexity of PCD.
Customization Potential for Advanced Research
Section titled “Customization Potential for Advanced Research”The study highlights the need for precise control over physical dimensions and electrical contacts. 6CCVD’s in-house capabilities directly address these requirements:
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Large Area Films | Custom PCD wafers up to 125mm diameter. | Enables scale-up from research samples to industrial device fabrication (e.g., large-area sensor arrays). |
| Thickness Control | SCD/PCD films from 0.1 µm to 500 µm. | Allows researchers to optimize film thickness for specific device architectures (e.g., thin films for high-sensitivity sensors or thick films for power electronics). |
| Surface Termination | Precise control over CVD growth parameters. | We guarantee specific surface terminations (H-terminated for p-type surface conductivity, O-terminated for high resistivity) essential for tuning Ea and $\Phi_{GB}$. |
| Electrical Contacts | In-house custom metalization (Au, Pt, Ti, W, Cu). | We provide high-adhesion, low-resistance contacts (e.g., Au electrodes used in this study) directly patterned onto the diamond surface, simplifying device integration. |
| Surface Quality | Polishing services (Ra < 5 nm for inch-size PCD). | Ensures optimal surface morphology for subsequent lithography, metalization, and reliable sensor performance. |
Engineering Support
Section titled “Engineering Support”The core finding of this paper—that surface hydrogenation plays a crucial role in tuning transport properties for sensing and electronics—is a key area of expertise for 6CCVD. Our in-house PhD team specializes in:
- Material Selection: Assisting clients in choosing the optimal diamond grade (SCD vs. PCD) and thickness for specific electronic transport or gas sensing projects.
- Process Optimization: Tailoring CVD recipes to achieve precise hydrogen or boron doping levels necessary to meet target activation energies (Ea) or Density of States N(EF).
- Device Integration: Providing technical consultation on metalization schemes and surface preparation to ensure robust electrical performance in complex hetero-junction devices.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The polycrystalline diamonds were synthesized on n-type single crystalline Si wafer by Hot Filament CVD method. The structural properties of the obtained diamond films were checked by X-ray diffraction and Raman spectroscopy. The conductivity of n-Si/p-diamond, sandwiched between two electrodes, was measured in the temperature range of 90-300 K in a closed cycle cryostat under vacuum. In the temperature range of (200-300 K), the experimental data of the conductivity were used to obtain the activation energies Ea which comes out to be in the range of 60-228 meV. In the low temperature region i.e., below 200 K, the conductivity increases very slowly with temperature, which indicates that the conduction occurs via Mott variable range hopping in the localized states near Fermi level. The densities of localized states in diamond films were calculated using Mott’s model and were found to be in the range of 9×1013 to 5×1014eV−1cm−3 depending on the diamond’s surface hydrogenation level. The Mott’s model allowed estimating primal parameters like average hopping range and hopping energy. It has been shown that the surface hydrogenation may play a crucial role in tuning transport properties.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
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- 1989 - Resistivity of chemical vapor deposited diamond films [Crossref]
- 2000 - Hypothesis on the conductivity mechanism in hydrogen terminated diamond films [Crossref]
- 2019 - The influence of the space charge on The Ohm’s law conservation in CVD diamond layers [Crossref]