The n–Si/p–CVD Diamond Heterojunction

At a Glance

Metadata	Details
Publication Date	2020-08-10
Journal	Materials
Authors	Szymon Łoś, K. Paprocki, Mirosław Szybowicz, K. Fabisiak
Institutions	Kazimierz Wielki University in Bydgoszcz, Poznań University of Technology
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: n-Si/p-CVD Diamond Heterojunction

This document analyzes the research paper “The n-Si/p-CVD Diamond Heterojunction” to extract critical technical data and align the findings with the advanced material capabilities offered by 6CCVD.

Executive Summary

The research successfully characterized the electrical conduction mechanisms in polycrystalline CVD diamond (PCD) heterojunctions, providing crucial data for high-performance electronic and sensing applications.

Core Application: Validation of n-Si/p-CVD diamond heterojunctions as promising materials for high-temperature and chemically harsh environment sensing devices.
Conduction Mechanism: Electrical transport (I-V-T, 77 K to 500 K) is governed by hopping through defects, transitioning from Schottky barrier control (low voltage) to Poole-Frenkel emission (high voltage).
Material Quality Impact: Significant differences in I-V-T characteristics were directly correlated with engineered defect densities (N_d ranging from 2.1 x 10¹⁸ cm^-3 to 5.3 x 10¹⁸ cm^-3).
Defect Identification: Cathodoluminescence (CL) confirmed the presence of key radiative recombination centers, including the A-band (2.88 eV, dislocations), vacancy-related states (2.56 eV), and N-aggregates (2.05 eV).
Key Material Constant: A very low conduction activation energy (T₀ = 7.5 meV) was derived, indicating that conductivity is highly sensitive to temperature and biasing voltage.
Methodological Advance: A new model was proposed that accurately describes the current magnification effect and saturation across the entire voltage range, allowing for the calculation of charge localization strength.

Technical Specifications

The following hard data points were extracted from the experimental results and synthesis parameters:

Parameter	Value	Unit	Context
Diamond Layer Thickness	4-5	µm	Polycrystalline CVD film (p-type surface)
Substrate Type	n-type (100)	N/A	Silicon wafer
Synthesis Temperature	1000	K	Hot Filament CVD (HF CVD)
Reaction Pressure	60	mbar	Growth parameter
I-V-T Measurement Range	77.4-500	K	Electrical characterization temperature range
DFI Defect Concentration (N_d)	2.1 x 10¹⁸	cm^-3	Estimated from Raman FWHM (11.3 cm^-1)
DFII Defect Concentration (N_d)	5.3 x 10¹⁸	cm^-3	Estimated from Raman FWHM (15.6 cm^-1)
Hydrogen Termination Level	~18	vol.%	Calculated from Raman background slope
A-Band Defect Energy	2.88	eV	Cathodoluminescence (CL) peak (Dislocations)
Vacancy-Related Defect Energy	2.56	eV	Cathodoluminescence (CL) peak
N-Aggregates Defect Energy	2.05	eV	Cathodoluminescence (CL) peak (DFII sample only)
Conduction Activation Energy (T₀)	7.5	meV	Derived from conductance G thermal dependency
Correlation Coefficient (r)	0.9998	N/A	Fit quality for the proposed I-V-T model

Key Methodologies

The experimental procedure focused on precise material synthesis and comprehensive electrical and structural characterization:

Substrate Preparation: n-type (100) silicon wafers were mechanically polished with diamond paste to achieve enhanced diamond nucleation density, followed by standard cleaning.
CVD Synthesis: Polycrystalline diamond (PCD) films were grown using a Hot Filament CVD (HF CVD) reactor.
- Gas Composition: Methanol vapor diluted in hydrogen (CH₃OH/H₂ = 1.0 vol.% for DFI, 4.0 vol.% for DFII).
- Recipe Parameters: Total pressure of 60 mbar, substrate temperature of 1000 K, and gas flow rate of 100 sccm.
Structural Characterization:
- Raman Spectroscopy: Used a 488 nm Ar ion laser to analyze the diamond peak (1333 cm^-1) and G-band (1545 cm^-1), determining FWHM and estimating defect concentration (N_d ~ L^-3).
- SEM: Used a Jeol JSM-820 (25 kV) to observe surface morphology and microcrystal orientation ((111) vs. mixed).
Defect Analysis: Cathodoluminescence (CL) spectroscopy (30 kV electron beam) was performed at room temperature to map defect centers within the diamond band gap.
Device Fabrication: Samples were metalized with a gold (Au) electrode on both the diamond layer and the substrate side to ensure proper electrical contact.
Electrical Measurement: I-V-T characteristics were recorded in the forward configuration across a broad temperature range (77.4 K to 500 K) using a rectangular voltage wave (0.1 Hz frequency) and high-precision instruments (Keithley picoammeter).

6CCVD Solutions & Capabilities

The findings confirm that the performance of diamond heterojunction devices is critically dependent on precise control over material quality, defect engineering, and interface metalization—all core competencies of 6CCVD.

Applicable Materials

Research Requirement	6CCVD Solution & Material Recommendation	Technical Advantage
Material Base: Undoped Polycrystalline CVD Diamond (PCD)	High-Quality Polycrystalline Diamond (PCD) wafers.	We offer PCD plates up to 125mm in diameter, exceeding typical research scale requirements, enabling industrial prototyping.
Thickness Control: Thin layers (4-5 µm)	Precision Thickness PCD	Our standard PCD thickness range (0.1 µm - 500 µm) ensures exact replication of the active layer thickness required for optimal depletion layer formation and conduction modeling.
Defect Engineering: Tuning N_d (2.1 x 10¹⁸ to 5.3 x 10¹⁸ cm^-3)	Engineered PCD for Sensing	Our advanced MPCVD systems allow for precise control of growth parameters (gas ratio, pressure, temperature) to intentionally tune defect density and crystallinity, optimizing the material for specific hopping or Poole-Frenkel conduction regimes.
Substrate Integration: Diamond on n-type Si	Custom Heterojunction Substrates	We provide custom diamond deposition services on various substrates, including large-area silicon, with substrate thicknesses available up to 10mm.

Customization Potential

The successful replication and advancement of this research require highly controlled fabrication steps, which 6CCVD provides:

Custom Metalization: The paper utilized Gold (Au) electrodes. 6CCVD offers comprehensive, in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu. We can design and deposit multi-layer contact schemes (e.g., Ti/Pt/Au) optimized for high-temperature stability (up to 500 K, as tested in the paper) and low contact resistance.
Surface Finishing: While the paper used as-grown PCD, achieving uniform electrical contacts often requires superior surface quality. We offer advanced polishing services achieving Ra < 5 nm on inch-size PCD, ensuring highly uniform interfaces for reliable I-V-T measurements and device performance.
Custom Dimensions: We can supply PCD wafers up to 125mm, allowing researchers to scale up from small experimental coupons to full-scale device fabrication.

Engineering Support

6CCVD’s in-house PhD team specializes in the physics of CVD diamond defects and electrical transport. We can assist researchers and engineers with material selection and optimization for similar diamond heterojunction and high-temperature sensing projects. Our expertise ensures that the supplied material properties (e.g., specific defect concentrations, crystallinity, and surface termination) are precisely matched to the required device physics, minimizing development time.

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

View Original Abstract

Due to the possible applications, materials with a wide energy gap are becoming objects of interest for researchers and engineers. In this context, the polycrystalline diamond layers grown by CVD methods on silicon substrates seem to be a promising material for engineering sensing devices. The proper tuning of the deposition parameters allows us to develop the diamond layers with varying crystallinity and defect structure, as was shown by SEM and Raman spectroscopy investigations. The cathodoluminescence (CL) spectroscopy revealed defects located just in the middle of the energy gap of diamonds. The current-voltage-temperature, I−V−T characteristics performed in a broad temperature range of 77-500 K yielded useful information about the electrical conduction in this interesting material. The recorded I−V−T in the forward configuration of the n-Si/p-CVD diamond heterojunction indicated hopping trough defects as the primary mechanism limiting conduction properties. The Ohmic character of the carriers flux permitting throughout heterojunction is intensified by charges released from the depletion layer. The magnification amplitude depends on both the defect density and the probability that biasing voltage is higher than the potential barrier binding the charge. In the present work, a simple model is proposed that describes I−V−T characteristics in a wide range of voltage, even where the current saturation effect occurs.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13163530

References

2017 - Analysis of the reverse I-V characteristics of diamond-based PIN diodes [Crossref]
2018 - A 4.5 μm PIN diamond diode for detecting slow neutrons [Crossref]
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1990 - The Effect of Surface Treatment on the Electrical Properties of Metal Contacts to Boron-Doped Homoepitaxial Diamond Film [Crossref]
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2013 - The Undoped CVD Diamond Electrode: The Effect of Surface Pretreatment on its Electrochemical Properties [Crossref]
2010 - Electron paramagnetic resonance and Raman spectroscopy characterization of diamond films fabricated by HF CVD method [Crossref]
2012 - The influence of working gas on CVD diamond quality [Crossref]
2011 - Electrochemical properties of undoped CVD diamond films [Crossref]