The Charge Transport Properties of Polycrystalline CVD Diamond Films Deposited on Monocrystalline Si Substrate

At a Glance

Metadata	Details
Publication Date	2025-10-07
Journal	Coatings
Authors	K. Paprocki, K. Fabisiak, Szymon Łoś, W. Kozera, Tomasz Knapowski
Institutions	Bydgoszcz University of Science and Technology, AGH University of Krakow
Analysis	Full AI Review Included

Technical Documentation & Analysis: Charge Transport in CVD Diamond Heterojunctions

This document analyzes the research paper “The Charge Transport Properties of Polycrystalline CVD Diamond Films Deposited on Monocrystalline Si Substrate” to provide technical specifications and highlight how 6CCVD’s advanced MPCVD capabilities can replicate, optimize, and extend this research for high-performance electronic applications.

Executive Summary

The study investigates the electronic transport mechanisms in p-diamond/n-Si heterojunctions, revealing critical limitations related to polycrystalline diamond quality.

Application Focus: Fabrication and electrical characterization of diamond/silicon heterojunctions for potential rectifying diodes and radiation detectors.
Core Challenge Identified: Undoped Polycrystalline CVD (PCD) films grown via Hot Filament CVD (HF CVD) exhibit extremely low hole mobility (ranging from 0.00143 to 0.01867 cm²/Vs).
Limiting Factor: Mobility is dominated and severely restricted by grain boundaries, structural defects, and high densities of deep trap states (up to 8.9 x 10¹⁶ eV^-1cm^-3).
Electrical Behavior: Devices display diode-like rectifying behavior, with transport governed by thermionic emission (junction-limited) at low bias and space-charge-limited conduction (SCLC) (bulk-limited) at high bias.
Quality Correlation: Higher structural quality (narrower Raman FWHM, higher Q factor) directly correlated with lower trap density and improved rectifying behavior (lower ideality factor, n = 1.6 minimum).
6CCVD Value Proposition: 6CCVD specializes in high-purity MPCVD diamond, offering Single Crystal Diamond (SCD) or optimized PCD that significantly reduces the grain boundary effects and trap densities observed in this HF CVD study, enabling superior charge transport characteristics.

Technical Specifications

The following hard data points were extracted from the analysis of the p-diamond/n-Si heterojunctions:

Parameter	Value Range	Unit	Context
Diamond Layer Thickness	4-6	µm	Polycrystalline CVD film
Substrate Type	(100) n-type Si	N/A	Resistivity: 3.5 Ω·cm
Growth Method Used	Hot Filament CVD (HF CVD)	N/A	Lower quality precursor to MPCVD
Ideality Factor (n)	1.6 to 6.4	N/A	Determined from I-V characteristics (0-0.3 V)
Hole Mobility ($\mu_p$)	0.00143 to 0.01867	cm²/Vs	Extracted via SCLC analysis (low mobility)
Deep Trap Density ($N_t$)	0.5 to 8.9 x 10¹⁶	eV^-1cm^-3	Estimated from ideality factor and SCLC
Diamond Quality (Q)	97.65 to 98.90	%	Derived from Raman ID/IG ratio
Crystallite Size (L₍₂₂₀₎)	57 to 71	nm	Determined via XRD (Scherrer formula)
Measurement Temperature	Room Temperature (RT)	N/A	I-V characteristics

Key Methodologies

The undoped polycrystalline diamond films were synthesized and characterized using the following primary steps:

Substrate Preparation: (100) n-type Si substrates (3.5 Ω·cm) were polished with 0.2 µm diamond paste.
Seeding: Substrates were seeded in an ultrasonic bath using nano/microdiamond powders in methanol (30 min), followed by cleaning with alcohol and acetone.
Growth Method: Hot Filament CVD (HF CVD) was utilized.
Growth Parameters (Typical Range):
- Filament Temperature: 2300 ± 50 K (Tungsten).
- Substrate Temperature: 980 ± 30 K.
- Gas Flow Rate: 100 ± 5 sccm.
- Gas Mixture: 2.3%-2.75% CH₄/H₂ ratio.
- Deposition Pressure: 20 to 100 mbar.
Contact Metalization: Gold (Au) contacts (5 mm diameter) were thermally evaporated onto the diamond surface and the backside of the Si substrates.
Characterization: Structural quality was assessed using SEM, XRD, and Raman spectroscopy (488 nm laser). Electrical transport was analyzed via I-V measurements at room temperature using a Keithley 6485 picoammeter.

6CCVD Solutions & Capabilities

The research clearly demonstrates that the performance of diamond/silicon heterojunctions is critically limited by the structural quality and defect density of the CVD diamond layer. 6CCVD’s advanced MPCVD technology provides the necessary material quality to overcome these limitations, enabling high-performance device fabrication.

Applicable Materials for High-Performance Heterojunctions

The low mobility observed in the paper (0.00143 to 0.01867 cm²/Vs) is typical for HF CVD PCD. To achieve the high mobility and low trap density required for advanced electronic devices, 6CCVD recommends the following materials:

6CCVD Material	Recommendation Rationale	Key Benefit for Transport
Electronic Grade SCD	Ideal for maximizing carrier mobility and minimizing deep trap states. SCD eliminates grain boundaries, the dominant limiting factor identified in the paper.	Mobility comparable to natural diamond; ideality factor approaching unity (n ≈ 1).
High-Purity PCD	For applications requiring larger area or lower cost than SCD, 6CCVD’s MPCVD PCD offers superior crystalline quality and lower amorphous carbon content than HF CVD films.	Significantly reduced grain boundary scattering compared to the films studied.
Boron-Doped Diamond (BDD)	If the application requires controlled p-type doping beyond the unintentional p-type behavior of H-terminated undoped films.	Precise control over carrier concentration and conductivity for optimized junction design.

Customization Potential for Device Replication and Optimization

6CCVD’s in-house manufacturing capabilities directly address the material and fabrication requirements of this research, offering significant advantages over standard CVD suppliers.

Requirement in Paper	6CCVD Capability	Optimization Advantage
Thickness (4-6 µm)	SCD/PCD thickness control from 0.1 µm up to 500 µm.	Precise control over the diamond layer thickness (d) is crucial for optimizing SCLC transport (J $\propto$ 1/d³).
Substrate Size	Plates/wafers up to 125 mm (PCD).	Enables scaling of the p-diamond/n-Si heterojunctions to industrial wafer sizes.
Metal Contacts (Au)	Internal metalization services (Au, Pt, Pd, Ti, W, Cu).	Custom, high-quality ohmic or Schottky contacts can be deposited to minimize interface resistance and optimize barrier height.
Surface Finish	Polishing capability: Ra < 1 nm (SCD), Ra < 5 nm (Inch-size PCD).	Ultra-smooth surfaces are critical for minimizing interface defects and inhomogeneities that affect barrier height and ideality factor.
Growth Method	Advanced Microwave Plasma CVD (MPCVD).	MPCVD offers higher purity, lower growth temperatures, and better control over crystalline quality compared to the HF CVD method used in the study.

Engineering Support

The correlation between structural quality (Raman FWHM, Q factor) and electronic performance (mobility, trap density) is a complex engineering challenge. 6CCVD’s in-house PhD team specializes in diamond material science and device physics. We offer comprehensive engineering consultation to assist researchers and engineers in:

Selecting the optimal diamond grade (SCD vs. PCD) based on required mobility and trap density specifications.
Designing custom metalization stacks (e.g., Ti/Pt/Au) for specific ohmic or rectifying contact requirements.
Optimizing growth parameters to achieve the lowest possible ideality factors and highest charge collection efficiency for radiation detector or diode applications.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 diodes—including the ideality factor (n) and carrier mobility (μ)—were 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 × 1015 and 8 × 1016 eV−1·cm−3. These variations were attributed to differences in the structural quality of the diamond layers and the effects of surface hydrogen termination.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings15101171

References

2004 - Charge collection distance measurements in single and polycrystalline CVD diamond [Crossref]
1992 - Electrical transport properties of undoped CVD diamond films [Crossref]
1998 - Comparison of the hole mobility in undoped and boron-doped polycrystalline CVD diamond films [Crossref]
2009 - Electronic and optical properties of boron-doped nanocrystalline diamond films [Crossref]
2022 - Current transient spectroscopic study of vacancy complexes in diamond Schottky pin diode [Crossref]
2014 - Contactless photoconductance study on undoped and doped nanocrystalline diamond films [Crossref]
1999 - Doping of diamond [Crossref]