Growth of synthetic diamond films and their electrophysical properties

At a Glance

Metadata	Details
Publication Date	2023-12-26
Journal	UNEC journal of engineering and applied sciences
Authors	Asef Nabiyev, J. I. Huseynov
Institutions	Azerbaijan State Pedagogical University
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance Diamond Semiconductors

Executive Summary

This document analyzes the research on the growth and electrophysical properties of synthetic diamond films, focusing on the creation of highly conductive p-type layers via Boron ion implantation and surface hydrogenation for Field-Effect Transistor (FET) applications.

Material Perfection: Homoepitaxial Single Crystal Diamond (SCD) structures grown by MPCVD demonstrate high material perfection suitable for wide-temperature range semiconductive devices.
P-Type Doping: Boron (B⁺) ion implantation, followed by high-temperature annealing (up to 1500°C), successfully created p-type conducting layers in diamond.
High Mobility: Record hole mobility values were achieved in implanted CVD diamond, reaching 520 cm²/(V·s) in the experimental samples, with cited literature values up to 1150 cm²/(V·s).
Surface Conductivity: A simpler, more reproducible method for forming a p-type conductive layer was demonstrated via thermal treatment in a hydrogen atmosphere (900°C), yielding mobilities of 150-200 cm²/(V·s).
Device Demonstration: A Field-Effect Transistor (FET) was successfully fabricated on the hydrogenated diamond surface, demonstrating low gate leakage and current modulation up to a maximum gate voltage of 5 V.
Activation Energy: Electrical conductivity analysis revealed extremely low activation energies for implanted boron, ranging from E_a = 0.03 eV to 0.07 eV, confirming high conductivity at room temperature.

Technical Specifications

Parameter	Value	Unit	Context
CVD Gas Mixture	2% CH₄ - 98% H₂	%	Standard MPCVD growth recipe
CVD Substrate Temperature	500 - 900	°C	Range for film formation process
CVD Residual Pressure	0.14 - 0.4	Pa	Low-pressure plasma discharge
Film Growth Rate (Cited)	1 - 2	µm/h	Weak point of conventional CVD method
B⁺ Implantation Energy (Range)	10 - 350	keV	Energies used for creating conducting layers
B⁺ Implantation Dose (High)	5.0 x 10¹⁵	cm^-2	Used to create buried conducting layers
Post-Implantation Annealing T	1380 or 1500	°C	Required for lattice recovery and electrical activation
Hole Mobility (B-Implanted, Max)	520	cm²/(V·s)	Achieved in Sample 5 (high N concentration)
Hole Mobility (H-Surface)	150 - 200	cm²/(V·s)	Achieved via 900°C H₂ thermal treatment
Boron Activation Energy (Low T)	0.03	eV	Lowest observed E_a in implanted diamond
FET Gate Dielectric Thickness	200	nm	Non-conducting near-surface layer
FET Gate Metal Thickness	60	nm	Copper (Cu) layer deposited by resistive evaporation
FET Maximum Gate Voltage	5	V	Demonstrated stable operation

Key Methodologies

The research utilized Microwave Plasma Chemical Vapor Deposition (MPCVD) for diamond film growth, followed by advanced post-processing techniques to control conductivity.

CVD Growth: Single crystal diamond films were grown homoepitaxially using MPCVD. The process involved decomposition of a 2% CH₄ - 98% H₂ gas mixture at residual pressures of 0.14 - 0.4 Pa and substrate temperatures up to 900°C.
Boron Ion Implantation: B⁺ ions were implanted at various energies (10 keV to 350 keV) and doses (up to 5 x 10¹⁵ cm^-2) to create near-surface or buried p-type conducting layers. Aluminum masks (30-80 nm thick) were used in some experiments to control the depth profile.
Post-Implantation Annealing: Implanted samples were subjected to high-temperature annealing (1380°C or 1500°C) for 1 to 60 minutes to repair crystal lattice damage and electrically activate the interstitial boron atoms.
Hydrogenation (H-Layer Formation): SCD plates were mechanically polished (Ra < 5 nm) and annealed in a hydrogen atmosphere at 900°C for 20 minutes to form a stable, reproducible p-type conductive surface layer.
FET Fabrication: A MIS-transistor structure was created on the hydrogenated surface. A 200 nm non-conducting diamond layer served as the dielectric. Copper (Cu) was deposited via resistive evaporation and patterned using photolithography to form the gate (L=35 µm, W=1 mm).
Characterization: Electrophysical properties were measured using the Van der Pauw method (specific conductivity vs. temperature) and Hall measurements (hole concentration and mobility).

6CCVD Solutions & Capabilities

The research demonstrates the critical need for high-quality, defect-controlled SCD material for advanced semiconductor devices like FETs. 6CCVD is uniquely positioned to supply the necessary materials and customization services to replicate and extend this research into commercial applications.

Applicable Materials

To replicate the high-performance results achieved in this study, 6CCVD recommends the following materials:

Research Requirement	6CCVD Material Solution	Key Benefit
Homoepitaxial Substrate	Optical Grade SCD (Single Crystal Diamond)	Extremely low defect density, high purity, and preferred (100) orientation for optimal device layer growth.
P-Type Conducting Layer	Boron-Doped Diamond (BDD) - SCD or PCD	For applications requiring bulk conductivity, 6CCVD offers in-situ BDD growth, eliminating the lattice damage and high-temperature annealing steps required by ion implantation.
High-Power Substrates	High Thermal Conductivity SCD/PCD	Diamond’s record thermal conductivity is essential for heat abstraction in high-current/high-voltage electronics, as noted in the paper. 6CCVD provides substrates up to 10mm thick.

Customization Potential

6CCVD’s advanced manufacturing capabilities directly address the specific engineering requirements detailed in the paper, particularly concerning dimensions, surface quality, and integration.

Custom Dimensions: While the paper used small plates (3-3.5 mm), 6CCVD offers SCD and PCD plates/wafers up to 125mm in diameter, enabling scaling for production-level microelectronics.
Precision Polishing: The research required mechanical polishing to Ra < 5 nm. 6CCVD guarantees ultra-smooth polishing for SCD (Ra < 1 nm) and inch-size PCD (Ra < 5 nm), ensuring optimal surface quality for subsequent hydrogenation and metal gate deposition.
Integrated Metalization: The FET fabrication required the deposition of a Copper (Cu) gate. 6CCVD offers internal metalization services including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to receive fully processed, ready-to-use diamond structures, minimizing external processing steps.
Thickness Control: The study utilized thin layers (200 nm dielectric, 60 nm gate). 6CCVD provides precise thickness control for SCD and PCD films ranging from 0.1 µm up to 500 µm, tailored for specific device architectures.

Engineering Support

The successful creation of a diamond FET relies heavily on precise control over doping profiles, surface termination (hydrogenation), and post-growth processing.

Doping Expertise: 6CCVD’s in-house PhD team specializes in controlling boron concentration and distribution, offering consultation on the trade-offs between ion implantation (used in the paper) and highly uniform in-situ Boron-Doped Diamond (BDD) growth for similar Field-Effect Transistor (FET) and high-frequency device projects.
Process Optimization: We provide technical assistance in selecting the optimal SCD crystal orientation and surface preparation methods to maximize hole mobility and ensure reproducible p-channel formation via hydrogenation.
Global Supply Chain: 6CCVD ensures reliable, global shipping (DDU default, DDP available) of high-purity SCD and PCD materials, supporting international research and development efforts.

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

View Original Abstract

The possibilities of formation of single-crystal homoepitaxial diamond structures grown by the method of vapor-phase chemical deposition are investigated. Optimal technological conditions for the formation of structures are suggested. The layer with p-type conductivity formation process depending on the temperature and time is determined. It was shown that applied thermal treatment method in hydrogen can be an alternative to the conventional method of H layer formation in microwave hydrogen plasma due to simpler and more reproducible. The profile distribution of boron atoms in a diamond crystal was determined under different implantation modes. The temperature dependence of specific conductivity in the temperature range 80-700 K was studied, and the activation energy was calculated. The results of Hall measurements of the electrophysical parameters of implanted samples are presented, and the effect of nitrogen concentration on the electrophysical parameters is revealed. The electrophysical parameters of the structures obtained under various modes of ion implantation of boron in a crystal and subsequent annealing are presented. The possibility of creating a field effect transistor on a hydrogenated diamond surface is shown. The current-voltage characteristic of the manufactured sample was studied and it was shown that it demonstrates low leakage through the gate.

Tech Support

Original Source

DOI: https://doi.org/10.61640/ujeas.2023.1211