The Charge Transport Properties of Polycrystalline CVD Diamond Films Deposited on Monocrystalline Si Substrate
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-10-07 |
| Journal | Coatings |
| Authors | K. Paprocki, K. Fabisiak, Szymon ĆoĆ, W. Kozera, Tomasz Knapowski |
| Institutions | PoznaĆ University of Technology, University of Bydgoszcz |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the structural quality and charge transport mechanisms in undoped polycrystalline CVD diamond films deposited directly onto n-type silicon (Si) substrates, forming p-diamond/n-Si heterojunctions.
- Core Achievement: Successful fabrication and electrical characterization of p-diamond/n-Si heterojunctions exhibiting rectifying diode behavior, with transport mechanisms analyzed via Thermionic Emission (TE) and Space-Charge-Limited Conduction (SCLC) theories.
- Quality Correlation: A strong inverse correlation was established between structural quality (Raman Q factor) and trap state density, confirming that higher crystalline perfection leads to superior electronic performance.
- Transport Limitation: Charge transport is dominated by bulk defects within the polycrystalline diamond layer (SCLC regime), rather than the junction interface, limiting performance.
- Ideality Factor: Measured ideality factors (n) were high, ranging from 1.6 to 6.4, indicating significant deep trap states with densities between 0.5 x 1016 and 8.9 x 1016 eV-1cm-3.
- Mobility: Extracted hole mobilities (”p) were low (0.00143 to 0.01867 cm2/Vs), confirming that grain boundary trapping is the dominant mobility-limiting factor in these CVD films.
- Best Sample Performance: Sample PDF15 exhibited the highest structural quality (Q = 98.90%) and the best electrical performance (lowest n = 1.6, highest ”p = 0.01867 cm2/Vs).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Film Thickness | 4-6 | ”m | Polycrystalline CVD films |
| Si Substrate Type | (100) n-type | Orientation/Type | Resistivity: 3.5 Ω·cm |
| Filament Temperature | 2300 ± 50 | K | HF CVD growth parameter |
| Substrate Temperature | 980 ± 30 | K | HF CVD growth parameter |
| Gas Flow Rate | 100 ± 5 | sccm | Total flow rate |
| CH4/H2 Ratio Range | 2.30 - 2.75 | % | Varies by sample |
| Deposition Pressure Range | 20 - 100 | mbar | Varies by sample |
| Crystallite Size Range (L(220)) | 57 - 71 | nm | Determined by XRD (Scherrer formula) |
| Diamond Quality (Q) Range | 97.65 - 98.90 | % | Estimated via Raman spectroscopy |
| Raman Peak Position | 1331.5 | cm-1 | Characteristic diamond peak |
| Ideality Factor (n) Range | 1.6 - 6.4 | Dimensionless | Thermionic Emission regime (0-0.3 V) |
| Trap Density (Nt) Range | 0.519 - 8.915 | x 1016 eV-1cm-3 | Calculated from ideality factor |
| Hole Mobility (”p) Range | 0.00143 - 0.01867 | cm2/Vs | Extracted from SCLC regime |
| Diamond Bandgap (Eg) | 5.47 | eV | Intrinsic property of diamond |
Key Methodologies
Section titled âKey MethodologiesâThe polycrystalline diamond films were synthesized using the Hot Filament Chemical Vapor Deposition (HF CVD) method, followed by comprehensive structural and electrical characterization.
- Substrate Preparation:
- (100)-oriented n-type Si substrates (3.5 Ω·cm) were used.
- Polishing was performed using 0.2 ”m diamond paste.
- Seeding involved immersion in an ultrasonic bath containing nano/microdiamond powders in methanol (30 min).
- Final cleaning utilized alcohol and acetone (5 min).
- HF CVD Deposition Parameters:
- Filament Material/Temperature: Tungsten, 2300 ± 50 K.
- Substrate Temperature: 980 ± 30 K.
- Gas Mixture: CH4/H2 (2.3%-2.75% CH4 ratio).
- Total Gas Flow Rate: 100 ± 5 sccm.
- Deposition Pressure: Varied between 20 and 100 mbar.
- Deposition Rate: Approximately 0.4-0.5 ”m/h.
- Device Fabrication:
- Gold contacts (5 mm diameter) were thermally evaporated onto both the diamond surface and the backside of the Si substrate to form the heterojunction device.
- Structural Characterization:
- Morphology: Scanning Electron Microscopy (SEM).
- Crystalline Structure: X-ray Diffraction (XRD) used to determine crystallite sizes (57-71 nm) via the Scherrer formula on the (220) reflection.
- Quality Assessment: Raman spectroscopy (488 nm laser) used to calculate the Diamond Quality Q factor based on the ratio of the diamond peak (ID) to the amorphous carbon G-band (IG).
- Electrical Characterization:
- I-V characteristics were measured at room temperature (RT) using an Oxford Optistat cryostat.
- Transport analysis focused on three regimes: Ohmic (J proportional to V), Thermionic Emission (In(J) proportional to V), and Space-Charge-Limited Conduction (SCLC, J proportional to V2).
- Key parameters (ideality factor $n$, trap density $N_t$, and hole mobility $\mu_p$) were extracted from the slopes of the I-V and J-V2 plots.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of robust diamond/silicon heterojunctions is critical for next-generation electronics that require extreme performance characteristics.
- High-Power and High-Frequency Devices:
- Rectifying Diodes and Schottky Devices: Utilizing diamondâs high breakdown voltage and high thermal conductivity (superior heat dissipation) for power electronics operating above 300 °C.
- RF/Microwave Components: Leveraging the low dielectric constant for high-frequency applications.
- Radiation Hard Electronics:
- Radiation Detectors: Diamondâs superior radiation hardness makes it ideal for sensors and electronics used in space, nuclear reactors, and high-energy physics experiments where conventional silicon devices fail due to defect accumulation.
- Extreme Environment Sensors:
- High-Temperature Sensing: The wide bandgap ensures stable electronic operation in environments exceeding the limits of Si and SiC.
- Optoelectronics:
- UV Emitters and Detectors: Potential use in deep UV applications, although controlling defect states (which limit mobility) is essential for achieving high quantum efficiency.
View Original Abstract
In this work, diamond/Si heterojunctions were fabricated by synthesizing a diamond layer directly on a monocrystalline n-type Si substrate. The diamond layers were characterized using micro-Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The current-voltage (I-V) characteristics of the heterojunctions were measured at room temperature. The heterojunctions exhibited rectifying behavior, confirming their diode-like nature. Based on thermionic emission theory, key electrical parameters of the heterojunction diodesâincluding the ideality factor (n) and carrier mobility (ÎŒ)âwere estimated from the I-V characteristics. The I-V curves revealed large ideality factors ranging from 1.5 to 6.5, indicating the presence of deep trap states with densities between 2 Ă 1015 and 8 Ă 1016 eVâ1·cmâ3. These variations were attributed to differences in the structural quality of the diamond layers and the effects of surface hydrogen termination.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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