The Influence of Process Parameters on Hydrogen-Terminated Diamond and the Enhancement of Carrier Mobility

At a Glance

Metadata	Details
Publication Date	2024-12-30
Journal	Materials
Authors	Xingqiao Chen, Mingyang Yang, Yuanyuan Mu, Chengye Yang, Zhenglin Jia
Institutions	University of Chinese Academy of Sciences, Chinese Academy of Sciences
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Mobility Hydrogen-Terminated Diamond

Executive Summary

This research successfully demonstrates a methodology using Microwave Plasma Chemical Vapor Deposition (MPCVD) to achieve record-high carrier mobility in hydrogen-terminated single-crystal diamond (H-Diamond) films. This breakthrough is critical for next-generation high-power and high-frequency electronic devices.

Record Mobility Achieved: Optimized homoepitaxial growth resulted in a peak carrier mobility of 395 cm²/(Vs), significantly exceeding the typical 50-200 cm²/(Vs) range for H-Diamond.
Material Optimization: High-quality SCD films were grown homoepitaxially using 4% CH₄ concentration, which minimized crystal defects and nitrogen-vacancy (N-V) centers.
Surface Quality Control: Optimal surface roughness (RMS of 1.26 nm) was achieved by balancing growth and hydrogen etching effects, crucial for reducing surface scattering mechanisms that limit carrier transport.
Process Recipe Validation: The best electrical properties were obtained using a post-growth hydrogen plasma treatment at 900 °C for 30 minutes.
Application Potential: The resulting material exhibits low sheet resistance (7.82 kΩ/square) and enhanced carrier transmission, positioning it as an ideal choice for 2D hole gas (2DHG) conductive channels in diamond semiconductor devices.
6CCVD Relevance: The entire process relies on high-purity, low-defect SCD substrates and precise MPCVD control, core competencies of 6CCVD.

Technical Specifications

The following hard data points were extracted from the optimized experimental results (Sample 4, 4% CH₄, 30 min H-plasma treatment):

Parameter	Value	Unit	Context
Peak Carrier Mobility	395	cm²/(Vs)	Optimized H-terminated SCD
Sheet Resistance (Lowest)	7.82	kΩ/square	Optimized H-terminated SCD
Carrier Concentration	2.03 x 10¹²	/cm²	Measured at peak mobility
Surface Roughness (RMS)	1.26	nm	After 4% CH₄ epitaxial growth
Raman FWHM (4% CH₄)	2.21	cm^-1	Indicates high crystallinity and low defects
Substrate Material	SCD (100)	N/A	CVD Single-Crystal Diamond
Optimal CH₄ Concentration	4	%	For homoepitaxial growth
Optimal H-Plasma Treatment Temp	900	°C	Post-growth surface termination
Optimal H-Plasma Treatment Duration	30	min	Post-growth surface termination
Intrinsic Hole Mobility (Theoretical)	3800	cm²/(Vs)	Room temperature (Reference Data)

Key Methodologies

The high-mobility H-Diamond was fabricated using a multi-step MPCVD process focused on achieving high-quality homoepitaxy and precise surface termination.

Substrate Preparation:
- Substrates: CVD Single-Crystal Diamond (100) plane, 5 mm x 5 mm x 0.5 mm.
- Cleaning: Piranha solution (H₂O₂:H₂SO₄ = 3:7 volume ratio) for 4 h, followed by ultrasonic cleaning in deionized water and anhydrous ethanol.
Pre-Etching (Surface Purification):
- Process: Hydrogen plasma pre-etching.
- Temperature: Approximately 900 °C.
- Duration: 10 min.
- Purpose: Remove surface impurities (dust, non-diamond phase) and reduce stress damage from polishing.
Homoepitaxial Growth (High-Quality Layer):
- Method: MPCVD (6 kW system).
- Temperature Range: 950 °C-980 °C.
- Power Range: 4200-4600 W.
- Pressure Range: 13-15 kPa.
- Duration: 8 h.
- Key Parameter: CH₄ concentration was varied (1% to 5%); 4% CH₄ yielded the best crystal quality (lowest FWHM and RMS roughness).
Post-Growth Hydrogen Termination:
- Process: H₂ plasma etching (CH₄ turned off).
- Temperature: 900 °C.
- Duration: Varied (15 min, 30 min, 45 min).
- Purpose: Form stable C-H bonds for P-type surface conductivity (2DHG). 30 min treatment optimized surface smoothness (RMS 1.48 nm) and maximized carrier mobility.
Characterization:
- Crystal Quality: Raman spectroscopy (FWHM).
- Morphology/Roughness: Atomic Force Microscopy (AFM, RMS).
- Electrical Properties: Hall test system (Carrier type, concentration, mobility, sheet resistance).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials and custom processing required to replicate and advance this high-mobility H-Diamond research. Our expertise in MPCVD growth and post-processing ensures optimal material performance for advanced electronic applications.

Applicable Materials

To replicate the high-quality homoepitaxial growth demonstrated in this paper, researchers require the highest quality SCD substrates.

Optical Grade Single Crystal Diamond (SCD): 6CCVD provides high-purity, low-defect SCD substrates essential for homoepitaxial growth. Our SCD material is available in thicknesses from 0.1 µm up to 500 µm, ensuring a perfect foundation for high-performance 2DHG devices.
Ultra-Smooth Polishing: The paper highlights the critical role of surface roughness (RMS < 2 nm) in achieving high carrier mobility. 6CCVD guarantees SCD polishing to an industry-leading standard of Ra < 1 nm, minimizing surface scattering mechanisms.
Custom SCD Substrates: We can supply the specific (100) orientation substrates used in this study, or alternative orientations as required for different device architectures.

Customization Potential

The success of this research hinges on precise control over growth parameters and surface termination. 6CCVD offers comprehensive custom services to meet these exact needs:

Research Requirement	6CCVD Custom Capability	Benefit to Client
Custom Dimensions	Plates/wafers up to 125 mm (PCD) and custom SCD sizes.	Facilitates scaling from R&D (5x5 mm) to commercial wafer sizes.
Precise Thickness Control	SCD layers grown from 0.1 µm to 500 µm.	Allows precise control over the epitaxial layer thickness (e.g., 18 µm layer achieved in the paper).
Custom MPCVD Recipes	In-house expertise to tune CH₄ concentration, temperature, and pressure.	Enables replication of the optimal 4% CH₄ recipe and exploration of new growth windows.
Surface Termination/Etching	Custom hydrogen plasma treatment and etching services.	We can perform the critical 900 °C, 30 min H-plasma termination step in a controlled environment.
Metalization	Internal capability for Au, Pt, Pd, Ti, W, Cu deposition.	Essential for creating ohmic contacts and Hall test structures (as required for electrical characterization).

Engineering Support

6CCVD’s in-house PhD team specializes in wide bandgap semiconductor physics and MPCVD growth. We can assist with material selection and process optimization for similar Hydrogen-Terminated Diamond FET (Field-Effect Transistor) projects.

Process Consultation: Our engineers can help clients define the optimal pre-etching and post-growth H-termination parameters to maximize carrier mobility for specific device designs.
Quality Assurance: We provide detailed characterization data (Raman FWHM, AFM RMS) with every order, ensuring the material quality meets the stringent requirements for high-performance 2DHG channels.

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

View Original Abstract

With the development of diamond technology, its application in the field of electronics has become a new research hotspot. Hydrogen-terminated diamond has the electrical properties of P-type conduction due to the formation of two-dimensional hole gas (2DHG) on its surface. However, due to various scattering mechanisms on the surface, its carrier mobility is limited to 50-200 cm2/(Vs). In this paper, the effects of process parameters (temperature, CH4 concentration, time) on the electrical properties of hydrogen-terminated diamond were studied by microwave plasma chemical vapor deposition (CVD) technology, and hydrogen-terminated diamond with a high carrier mobility was obtained. The results show that homoepitaxial growth of a diamond film on a diamond substrate can improve the carrier mobility. Hydrogen-terminated diamond with a high carrier mobility and low sheet resistance can be obtained by homoepitaxial growth of a high-quality diamond film on a diamond substrate with 4% CH4 concentration and hydrogen plasma treatment at 900 ℃ for 30 min. When the carrier concentration is 2.03 × 1012/cm2, the carrier mobility is 395 cm2/(Vs), and the sheet resistance is 7.82 kΩ/square, which greatly improves the electrical properties of hydrogen-terminated diamond. It can enhance the transmission characteristics of carriers in the conductive channel, and is expected to become a potential material for application in devices, providing a material choice for its application in the field of semiconductor devices.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18010112

References

2020 - Diamond semiconductor performances in power electronics applications [Crossref]
2023 - Superconductivity at 117 K inH-doped diamond [Crossref]
2020 - Effects of hydrogen termination of CVD diamond layers [Crossref]
2021 - Surface transfer doping of diamond: A review [Crossref]
2013 - Electrical properties of the high quality boron-doped synthetic single-crystal diamonds grown by the temperature gradient method [Crossref]
2023 - Temperature dependence of two-dimensional hole gas on hydrogen-terminated diamond surface [Crossref]
2023 - Fabrication of hydroxyl terminateddiamond by high-voltage hydroxide ion treatments [Crossref]
2024 - Surface transfer doping of hydrogen-terminated diamond probed by shallow nitrogen-vacancy centers [Crossref]
2018 - Mobility of two-dimen-sional hole gas in H-terminated diamond [Crossref]
2020 - Investigation of charge carrier trapping in H-terminated diamond devices [Crossref]