A reactive molecular dynamics study of the hydrogenation of diamond surfaces

At a Glance

Metadata	Details
Publication Date	2021-09-14
Journal	Computational Materials Science
Authors	Eliezer Fernando Oliveira, Mahesh R. Neupane, Chenxi Li, Harikishan Kannan, Xiang Zhang
Institutions	DEVCOM Army Research Laboratory, Universidade Estadual de Campinas (UNICAMP)
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: Hydrogenation on Diamond Surfaces

This document analyzes the findings of “A Reactive Molecular Dynamics Study of Hydrogenation on Diamond Surfaces” to provide technical specifications and align 6CCVD’s MPCVD diamond capabilities with the requirements for advanced electronic device research, specifically high-frequency Field-Effect Transistors (FETs).

Executive Summary

Core Research Goal: To determine the optimal low-index diamond surface orientation ((001), (013), (110), (113), (111)) for achieving maximum hydrogen coverage and stability, a critical step for realizing high-performance p-type diamond FETs.
Methodology: Fully atomistic Reactive Molecular Dynamics (FARMD) simulations were used to model hydrogenation dynamics across a temperature range of 500°C to 1200°C.
Key Finding: Optimal Orientation: The (113) and (013) surfaces demonstrated the highest capacity for hydrogen incorporation, reaching up to 17 H atoms/nm² at 1200°C due to high initial dangling bond densities.
Stability and Efficiency: The (113) surface is identified as the most promising candidate for electronic devices, exhibiting high hydrogen coverage and considerable passivation efficiency (up to 67% of initial dangling bonds passivated).
Electronic Implications: High hydrogen coverage results in a more negative electron affinity (NEA) and decreased work function (WF), essential for forming the p-type (hole) channel required in diamond FETs.
6CCVD Value Proposition: 6CCVD specializes in providing the high-purity, orientation-controlled Single Crystal Diamond (SCD) and large-area Polycrystalline Diamond (PCD) substrates, including custom Boron-Doped Diamond (BDD), necessary to experimentally validate and commercialize these findings.

Technical Specifications

The following data points were extracted from the MD simulations regarding surface characteristics and hydrogenation thresholds.

Parameter	Value	Unit	Context
Surfaces Investigated	(001), (013), (110), (113), (111)	N/A	Low indices diamond surfaces for FETs
Simulation Temperature Range	500 - 1200	°C	Thermal equilibration and hydrogenation
Typical Experimental Hydrogenation Range	700 - 900	°C	Common range for H plasma treatment
Max H Atoms Incorporated (1200°C)	17	H atoms/nm²	Achieved by (113) surface
Max H Atoms Incorporated (1200°C)	16	H atoms/nm²	Achieved by (013) surface
Dangling Bond Density (113/RT)	30	bonds/nm²	Highest initial density at Room Temperature (RT)
Dangling Bond Density (110/RT)	22	bonds/nm²	Most stable density across all temperatures
Max Hydrogenation Efficiency	67	%	Maximum percentage of initial dangling bonds passivated (at 1200°C)
Bulk C-C Bond Length (RT)	1.55 ± 0.03	Å	Standard sp³-sp³ bond characteristic
(001) Reconstructed Dimer Bond Length (RT)	1.42 ± 0.02	Å	sp²-sp² bond characteristic
Hydrogen Saturation Time	~50	ps	Required exposure time to reach saturation threshold

Key Methodologies

The study utilized advanced computational techniques to model the diamond surface reactions:

Simulation Framework: Fully Atomistic Reactive Molecular Dynamics (FARMD) simulations were performed using the ReaxFF force field, implemented in the computational LAMMPS code.
Surface Selection: Five pristine diamond surfaces were selected: (001), (013), (110), (113), and (111), chosen for their relevance in device applications and exposure during CVD growth.
Slab Configuration: Square diamond slabs (~5.4 x 5.4 nm² surface area, eight layers thick) were created. The bottom two layers were constrained to mimic bulk properties, while the top six layers were allowed to move freely.
Thermal Equilibration: Surfaces underwent energy minimization followed by thermal equilibration at five temperatures: Room Temperature (RT), 500°C, 700°C, 900°C, and 1200°C, using the Constant-Temperature, Constant-Volume (NVT) ensemble for 400 ps.
Hydrogenation Atmosphere: An atmosphere of randomly distributed atomic hydrogen atoms was created, with the total number of H atoms set to 120% higher than the available dangling bonds on the thermalized surface.
Hydrogenation Simulation: FARMD runs were executed for 2.0 ns at 500°C, 700°C, 900°C, and 1200°C (NVT ensemble), with a time step of 0.1 fs. The simulation box maintained an internal pressure of 1 atm.
Analysis Focus: Evaluation centered on dangling bond density, structural reconstruction, hydrogen incorporation rate, saturation threshold, and the formation of functional groups (-CH, -CH₂).

6CCVD Solutions & Capabilities

The findings of this MD study directly inform the material requirements for developing next-generation diamond FETs. 6CCVD is uniquely positioned to supply the necessary high-quality, customized diamond substrates for experimental validation and device prototyping.

Applicable Materials for Replication and Extension

Research Requirement	6CCVD Material Recommendation	Technical Rationale & Sales Advantage
Optimal Orientation (113) & (013)	Single Crystal Diamond (SCD) Substrates: High-purity, low-defect SCD wafers with precise orientation control (e.g., (113) or (013) cut).	Essential for replicating the theoretical model of pristine surfaces and achieving maximum, uniform hydrogen coverage (up to 17 H/nm²).
High-Frequency Device Scaling	Electronic Grade Polycrystalline Diamond (PCD): Wafers up to 125mm in diameter, polished to Ra < 5nm.	Enables the transition from small-scale SCD research to large-area, cost-effective manufacturing of high-power RF devices.
Enhanced p-Type Conductivity	Custom Boron-Doped Diamond (BDD): Available in both SCD and PCD formats.	The study references low electrical resistance in BDD (113). BDD substrates allow researchers to explore the synergistic effects of H-termination and bulk doping for superior hole channel formation.
Surface Quality and Stability	Ultra-Smooth Polishing (SCD: Ra < 1nm): Precision polishing services for all orientations.	Minimizes surface defects and scattering centers, ensuring the structural stability and homogeneous p-type conductivity predicted by the MD simulations.

Customization Potential

To move from theoretical modeling to functional FETs, precise material engineering is required. 6CCVD offers comprehensive customization services:

Custom Dimensions and Thickness: We provide plates and wafers up to 125mm (PCD) and offer precise thickness control for both SCD and PCD films (0.1µm to 500µm) and substrates (up to 10mm).
Orientation Control: We guarantee specific crystal orientations, such as the high-coverage (113) and stable (110) surfaces, critical for optimizing hydrogenation efficiency.
Advanced Metalization: FET fabrication requires robust contacts. 6CCVD offers in-house deposition of standard and custom metal stacks, including Au, Pt, Pd, Ti, W, and Cu, directly onto the H-terminated diamond surface.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in MPCVD growth and surface engineering. We offer consultation services to assist researchers in:

Selecting the optimal diamond grade (SCD vs. PCD) and orientation ((113) vs. (001)) based on specific device requirements (e.g., maximizing H-coverage for NEA or minimizing dangling bonds for stability).
Designing custom BDD doping profiles to achieve desired electrical resistance in hydrogenated diamond-based p-channel transistors.
Developing post-processing steps, such as plasma hydrogenation recipes, to maximize the formation of desired functional groups (CH vs. CH₂) for tuning electron affinity and work function.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.commatsci.2021.110859

References

2019 - Boron-oxygen complex yields n-type surface layer in semiconducting diamond [Crossref]
2017 - Deep depletion concept for diamond MOSFET [Crossref]
2018 - High-mobility diamond field effect transistor with a monocrystalline h-BN gate dielectric [Crossref]
2020 - Oxidized Si terminated diamond and its MOSFET operation with SiO 2 gate insulator [Crossref]
2019 - Radiofrequency performance of hydrogenated diamond MOSFETs with alumina [Crossref]
2021 - Study of the structural phase transition in diamond (100) & (111) surfaces [Crossref]
1996 - Hydrogen-terminated diamond surfaces and interfaces [Crossref]