Synthesis and electrical properties study of Ib type diamond single crystal co-doped with boron and hydrogen under HPHT conditions

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	Acta Physica Sinica
Authors	Yong Li, Zongbao Li, Song Mou-Sheng, Wang Ying, Xiaopeng Jia
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Boron-Hydrogen Co-Doped Diamond

Executive Summary

This research details the High-Pressure High-Temperature (HPHT) synthesis and electrical characterization of Single Crystal Diamond (SCD) co-doped with Boron (B) and Hydrogen (H). The findings provide critical insights into defect engineering for advanced diamond semiconductor applications.

Core Achievement: Successful synthesis of p-type SCD co-doped with B and H using the HPHT temperature gradient method (6.0 GPa, 1600 K).
Performance Enhancement: Hydrogen co-doping resulted in a significant increase in electrical conductivity and carrier concentration, improving these metrics by approximately 100 times compared to B-only doped diamond.
Material Properties: The resulting material exhibits robust p-type semiconductor behavior, achieving a room-temperature resistivity of 7.50 x 10⁵ Ω·cm and a Hall mobility of 740 cm²·V⁻¹·s⁻¹.
Mechanism Confirmation: FTIR spectroscopy confirmed the incorporation of hydrogen in the diamond lattice via sp³ C-H anti-symmetric (2920 cm⁻¹) and symmetric (2850 cm⁻¹) vibrations.
Defect Control: The introduction of B and H successfully suppressed nitrogen incorporation, reducing the final nitrogen concentration to 230 ppm.
Theoretical Validation: First-principles calculations confirmed that H co-doping modifies the band structure, merging impurity states with the valence band maximum, thereby enhancing charge transfer efficiency.

Technical Specifications

The following hard data points were extracted from the synthesis and characterization of the optimal B/H co-doped diamond sample (Sample C).

Parameter	Value	Unit	Context
Synthesis Pressure	6.0	GPa	HPHT Growth Condition
Synthesis Temperature	1600	K	HPHT Growth Condition
Catalyst System	Fe₆₄Ni₃₆-C	N/A	Metal solvent/Carbon source
Boron Additive Concentration	0.06	wt.%	Added as B powder
Hydrogen Additive Concentration	0.1	wt.%	Added as LiH powder
Electrical Type	P-type	N/A	Confirmed by Hall Effect
Resistivity (Room Temp)	7.50 x 10⁵	Ω·cm	B+H Co-doped SCD
Carrier Concentration (Room Temp)	1.24 x 10⁸	cm⁻³	B+H Co-doped SCD
Hall Mobility (Room Temp)	740	cm²·V⁻¹·s⁻¹	B+H Co-doped SCD
Conductivity Improvement	~100	Times	Relative to B-only doped diamond
C-H Bond FTIR Peak 1	2850	cm⁻¹	sp³ C-H symmetric vibration
C-H Bond FTIR Peak 2	2920	cm⁻¹	sp³ C-H anti-symmetric vibration
Final Nitrogen Concentration	230	ppm	Reduced from typical Ib type

Key Methodologies

The experiment utilized the HPHT temperature gradient method combined with advanced spectroscopic and electrical characterization techniques.

HPHT Setup: Diamond growth was conducted in a domestic SPD-6x1200 six-sided press, utilizing a pyrophyllite cell assembly.
Condition Control: Pressure was fixed at 6.0 GPa and temperature at 1600 K. Temperature calibration was achieved using a Pt6%Rh-Pt30%Rh thermocouple.
Doping Strategy: High-purity graphite was used as the carbon source. Boron powder and Lithium Hydride (LiH) powder were introduced into the Fe₆₄Ni₃₆ metal catalyst system to achieve B and H co-doping.
Growth Orientation: A 0.6 mm SCD seed crystal was used, with the high-quality (111) face selected as the primary growth surface, resulting in final crystals with dominant (111) octahedral morphology.
Purification: Post-growth, samples were treated in boiling aqua regia for 1 hour to ensure complete removal of residual metal catalyst and surface impurities.
Characterization: Fourier Transform Infrared Spectroscopy (FTIR) confirmed the chemical bonding structure. Hall effect measurements were performed at room temperature to determine carrier type, concentration, resistivity, and mobility.
Theoretical Modeling: First-principles calculations based on Density Functional Theory (DFT) using the VASP software were employed to analyze the formation energies of different dopant configurations (B/N, B/N/H) and the resulting band structures.

6CCVD Solutions & Capabilities

The research demonstrates the critical role of co-doping in achieving high-performance p-type diamond semiconductors. While the paper utilized HPHT, 6CCVD specializes in high-purity, highly controllable MPCVD diamond, which offers superior scalability and precision for advanced electronic applications.

Applicable Materials for Replication and Extension

To replicate or extend this research into scalable electronic devices, 6CCVD recommends the following materials:

Boron-Doped Diamond (BDD) - Single Crystal (SCD):
- Application: Ideal for high-mobility devices, quantum sensing, and high-power electronics where low defect density is paramount.
- Advantage: MPCVD allows for precise control of B doping concentration (from trace levels to heavy doping, achieving metallic conductivity) and superior crystalline quality compared to HPHT.
Boron-Doped Diamond (BDD) - Polycrystalline (PCD):
- Application: Suitable for large-area electrodes, heat spreaders, and industrial sensors requiring high conductivity over large surfaces.
- Advantage: 6CCVD offers BDD PCD wafers up to 125mm in diameter, enabling industrial-scale semiconductor processing far exceeding HPHT limitations.

Customization Potential for Advanced Research

6CCVD’s in-house capabilities directly address the requirements for advanced diamond semiconductor research, such as that presented in this paper:

Research Requirement	6CCVD Customization Service
Precise Doping Control	Custom BDD Recipes: We offer tailored BDD growth recipes, allowing engineers to fine-tune the B/C ratio and gas phase H₂ concentration to optimize carrier concentration and mobility, replicating or surpassing the co-doping effects observed.
Device Integration & Contacts	In-House Metalization: Critical for Hall effect measurements and device fabrication, 6CCVD provides custom metal stacks (e.g., Ti/Pt/Au, W/Au) deposited directly onto the diamond surface, ensuring low-resistance ohmic contacts.
Specific Dimensions	Custom Plates and Wafers: SCD and PCD plates available in custom dimensions and thicknesses (SCD: 0.1µm to 500µm; PCD: 0.1µm to 500µm). We also offer substrates up to 10mm thick.
Surface Preparation	Ultra-Precision Polishing: SCD surfaces polished to Ra < 1nm and inch-size PCD polished to Ra < 5nm, essential for high-resolution lithography and minimizing surface scattering effects on carrier mobility.

Engineering Support

This study highlights the complexity of defect engineering in diamond. 6CCVD’s in-house PhD team provides expert consultation to assist researchers transitioning from HPHT concepts to scalable MPCVD fabrication. We offer support in material selection, optimizing doping profiles, and designing custom metalization schemes for similar p-type diamond semiconductor projects.

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

View Original Abstract

Diamond is well known for its excellent properties, such as its hardness, high thermal conductivity, high electron and hole mobility, high breakdown field strength and large band gap (5.4 eV), which has been extensively used in many fields. However, its application in semiconductor area needs to be further understood, because it is irreplaceable by conventional semiconductor materials, especially in the extreme working conditions. In order to obtain diamond semiconductor with excellent electrical performances, diamond crystals co-doped with boron (B) and hydrogen (H) are synthesized in an FeNi-C system by temperature gradient growth (TGG) at pressure 6.0 GPa and temperature 1600 K. Fourier infrared spectra (FTIR) measurements displayed that H is the formation of sp3 CH2-antisymmetric and sp3 -CH2-symmetric vibrations in the obtained diamond. Furthermore, the corresponding absorption peaks of H element are located at 2920 cm-1 and 2850 cm-1, respectively. Hall effects measurements demonstrated that the co-doped diamond exhibited that p- type material semiconductor performance, and the conductivity of the co-doped diamond is significantly enhanced comparing tocompared with the conductivity of the B-doping diamond. The results indicated that the Hall mobility mobilities is nearly equivalent between B-doped and co-doped diamond crystals are nearly equivalent, while the concentrations of the carriers and conductivity of the co-doped diamonds are higher than those of the B-doped diamond crystals. It is also noticed that the nitrogen concentration of the co-doped diamond decreases obviously, when the H and B are introduced into the diamond structure. Additionally, the change of the conductivity is investigated by first-principles calculation. In the B-doping diamond, two impurity levels are located in the forbidden band with small gaps. These impurity states above the Fermi level couldcan trap the photo-excited electrons, while those below Fermi level can trap the photo-excited vacancies, improving the transfer of the photo-excited carriers to the reactive sites. With the H co-doped diamond, the two impurity states moved to the valance band maximum and merged into each other, which extends the valance band and improves the charge transfer efficiency. From the perspective of energy band, for the co-doped of B and N atoms co-doped diamond, the impurity states are contributed by N/B-2p states while the overlop and splitting of N/B-2p in the band gap appeared. For the H co-doped diamond, the splitting of the N/B-2p states vanishes and shifts to the lower energy level, which was due to the fact that the excess charge transferred from N to H. The calculation results above are in qualitatively agreement with experimental results. We hope that this investigation would be meaningful for the application of diamond in semiconductor field.

Tech Support

Original Source

DOI: https://doi.org/10.7498/aps.65.118103