Hydrogen-terminated and oxygen-terminated diamond metal-oxide-semiconductor field-effect transistors

At a Glance

Metadata	Details
Publication Date	2025-09-02
Journal	Functional Diamond
Authors	Jiangwei Liu
Institutions	National Institute for Materials Science
Analysis	Full AI Review Included

Diamond MOSFETs for Extreme Environments: Technical Analysis and 6CCVD Solutions

This technical documentation analyzes the findings regarding Hydrogen-terminated (H-diamond) and Boron-doped Oxygen-terminated (O-diamond) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), demonstrating diamond’s critical role in high-power, high-frequency, and high-temperature electronics.

Executive Summary

Material Validation: The research confirms MPCVD diamond as the leading wide-bandgap semiconductor for next-generation high-power, high-frequency (up to 70 GHz), and high-temperature electronic devices.
E-mode Logic Circuits: Successful fabrication of enhancement-mode (E-mode) H-diamond MOSFETs and subsequent demonstration of robust NOT and NOR logic circuits using D-mode/E-mode configurations.
Record Thermal Stability: Boron-Doped (B-diamond) O-terminated MOSFETs exhibited stable, efficient operation up to 300 °C (with reported stability up to 400 °C), validating their use in extreme thermal environments.
High Performance Metrics: H-diamond devices achieved high current densities (up to 1.35 A/mm) and high breakdown voltages (4266 V).
Exceptional On/Off Ratio: B-diamond O-MOSFETs demonstrated an on/off current ratio exceeding 10⁹ at both room temperature (RT) and 300 °C, marking the highest reported values to date for this material class.
Gate Stack Engineering: The transition between D-mode and E-mode operation was precisely controlled through the use of bilayer gate oxides (e.g., LaAlO₃/Al₂O₃) and specific annealing processes.

Technical Specifications

The following table summarizes the key performance metrics achieved by the H-diamond and B-doped O-diamond MOSFETs.

Parameter	Value	Unit	Context
Maximum Drain Current (I_D,max)	1.35	A/mm	H-diamond MOSFET (Reference [3])
Maximum Extrinsic Transconductance (g_m,max)	206	mS/mm	H-diamond MOSFET (Reference [3])
Cut-off Frequency (f_T)	70	GHz	H-diamond MOSFET (Reference [7])
Breakdown Voltage	4266	V	H-diamond MOSFET (Reference [14])
O-Diamond MOSFET I_D,max (300 °C)	-10.9	mA/mm	In-situ 300 °C annealed B-diamond
O-Diamond MOSFET On-Resistance (R_ON)	1.1	kΩ mm	In-situ 300 °C annealed B-diamond
O-Diamond MOSFET On/Off Ratio	> 10⁹	Ratio	RT and 300 °C operation
B-Doping Activation Energy	0.37	eV	O-diamond channel layer
H-Diamond E-mode Threshold Voltage (V_TH)	-5.0 ± 0.1	V	LaAlO₃/Al₂O₃/H-diamond MOSFET
Maximum Logic Gain	26.1	Ratio	H-diamond NOT circuit (V_DD = -25.0 V)
Minimum Gate Length (L_G)	2.0	µm	E-mode H-diamond MOSFET

Key Methodologies

The fabrication and optimization of the diamond MOSFETs relied on precise material engineering and processing techniques:

Material Foundation: High-quality Single Crystal Diamond (SCD) epitaxial layers were used as the base semiconductor material, grown via MPCVD (Microwave Plasma Chemical Vapor Deposition).
Doping Control: Boron doping was utilized to create p-type O-diamond channel layers, with acceptor concentrations ranging from approximately 10¹⁶ cm^-3 to 10¹⁷ cm^-3.
Surface Termination:
- H-diamond: Hydrogen termination was employed to induce a Two-Dimensional Hole Gas (2DHG) channel layer, essential for high-current D-mode operation.
- O-diamond: Oxygen termination was used for B-doped devices to achieve superior thermal stability and high-temperature operation.
Gate Oxide Stacks: Gate insulators were formed using Atomic Layer Deposition (ALD) (e.g., Al₂O₃) and Sputtering Deposition (SD) (e.g., LaAlO₃). Bilayer stacks (SD-LaAlO₃/ALD-Al₂O₃) were critical for achieving E-mode characteristics.
E-mode Transition Mechanism: The shift from D-mode to E-mode was achieved by annealing (150-350 °C) or specific oxide stacks, which introduced compensatory positive charges to reduce the 2DHG density in the channel.
Thermal Processing: High-temperature performance was enhanced through:
- Ex-situ annealing at 500 °C for 30 minutes.
- In-situ annealing at 300 °C, which significantly increased I_D,max and reduced R_ON by enhancing boron dopant activation.
Device Geometry: Devices featured micron-scale geometries, including gate lengths (L_G) as low as 2.0 µm, defined using laser lithography.

6CCVD Solutions & Capabilities

6CCVD specializes in providing the high-purity, custom-engineered MPCVD diamond materials necessary to replicate and advance the high-performance MOSFETs and logic circuits demonstrated in this research.

Applicable Materials

To achieve the performance metrics reported (e.g., 1.35 A/mm I_D,max and > 10⁹ On/Off ratio), researchers require ultra-high quality, low-defect diamond material.

Application Requirement	6CCVD Material Recommendation	Key Specification Match
H-diamond MOSFET Channel	Optical Grade Single Crystal Diamond (SCD)	SCD thickness control from 0.1 µm to 500 µm. Essential for low-defect epitaxial growth and high 2DHG mobility.
High-Temperature MOSFETs	Custom Boron-Doped Diamond (BDD)	Precise BDD doping control (10¹⁶ cm^-3 to 10¹⁷ cm^-3) to optimize activation energy (0.37 eV) for 300 °C+ operation.
Large-Area Power Electronics	Polycrystalline Diamond (PCD) Wafers	PCD available up to 125 mm diameter, providing superior thermal dissipation for high-power logic arrays and CMOS devices.

Customization Potential

The research highlights the necessity of precise geometry and advanced gate stack integration. 6CCVD provides comprehensive services to meet these demands:

Custom Dimensions: 6CCVD supplies SCD plates and PCD wafers up to 125 mm, allowing researchers to scale device geometries beyond the reported micron-scale dimensions (L_G = 2.0 µm).
Ultra-Smooth Surfaces: We guarantee SCD polishing to Ra < 1 nm, which is critical for achieving uniform surface termination (H- or O-) and minimizing interface scattering losses in the 2DHG channel.
Advanced Metalization: 6CCVD offers in-house deposition of critical metals (Au, Pt, Pd, Ti, W, Cu). This capability is vital for fabricating low-resistance Ohmic contacts and complex gate stacks required for both D-mode and E-mode diamond MOSFETs.
Substrate Thickness: We provide substrates up to 10 mm thick, ensuring mechanical stability and robust thermal management for high-power device testing.

Engineering Support

6CCVD’s in-house PhD team specializes in wide-bandgap semiconductor physics and device engineering. We offer consultation services to assist researchers in material selection, doping profile optimization, and surface preparation for similar Diamond MOSFET and Logic Circuit projects. Our global shipping network (DDU default, DDP available) ensures rapid delivery of custom materials worldwide.

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

View Original Abstract

Extensive research has been conducted on wide-bandgap semiconductor diamond for the advancement of high-power, high-frequency, and high-temperature electronic devices. The author has established long-term collaboration with Prof. Koide, focusing on producing p-type hydrogen-terminated diamond (H-diamond) and boron-doped oxygen-terminated diamond (O-diamond) based metal-oxide-semiconductor field-effect transistors (MOSFETs). This article presents our primary research findings on the fabrication of enhancement-mode H-diamond MOSFETs and MOSFET logic circuits, as well as the high-temperature operation of the boron-doped O-diamond MOSFETs.

Tech Support

Original Source

DOI: https://doi.org/10.1080/26941112.2025.2551496