Inversion-type p-channel diamond MOSFET issues

At a Glance

Metadata	Details
Publication Date	2021-08-04
Journal	Journal of materials research/Pratt’s guide to venture capital sources
Authors	Xufang Zhang, Tsubasa Matsumoto, Satoshi Yamasaki, Christoph E. Nebel, Takao Inokuma
Institutions	Kanazawa University
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: Inversion-Type p-Channel Diamond MOSFETs

Executive Summary

This documentation analyzes the fabrication and performance limitations of inversion-type p-channel diamond Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), highlighting 6CCVD’s capabilities to overcome current material and interface challenges.

Device Achievement: Successful fabrication of the world’s first normally-off inversion-channel homoepitaxial and heteroepitaxial diamond MOSFETs, critical for next-generation power electronics.
Primary Limitation: Low Field-Effect Mobility ($\mu_{FE}$) is primarily limited by extremely high Interface State Density ($D_{it}$), measured in the range of 4-9 $\times$ 10¹² cm⁻²eV⁻¹.
Material Solution: A novel OH-termination technique (H-diamond followed by wet annealing) was developed, demonstrating significant improvement in the Al₂O₃/diamond interface quality compared to traditional O-diamond termination.
Doping Control: Precise control of phosphorus (N-type) doping concentration ($N_p$) was achieved, ranging from 2 $\times$ 10¹⁵ to 6 $\times$ 10¹⁶ cm⁻³, enabling effective threshold voltage modulation.
Commercialization Pathway: Heteroepitaxial growth on Ir/Si substrates was successfully demonstrated to address the size and cost limitations of traditional High-Pressure High-Temperature (HPHT) diamond substrates.
6CCVD Value Proposition: 6CCVD provides the necessary large-area Polycrystalline Diamond (PCD) substrates (up to 125mm) and ultra-low roughness Single Crystal Diamond (SCD) polishing (Ra < 1 nm) required to scale production and enhance channel mobility.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Bandgap	5.5	eV	Ultra-wide bandgap material
Breakdown Electric Field	> 10	MV/cm	Superior physical property
Max Field-Effect Mobility ($\mu_{FE}$)	20	cm²V⁻¹s⁻¹	Homoepitaxial MOSFET (low $N_p$)
Max Field-Effect Mobility ($\mu_{FE}$)	2.7	cm²V⁻¹s⁻¹	Heteroepitaxial MOSFET
Target Mobility for Improvement	> 1000	cm²V⁻¹s⁻¹	Requires $D_{it}$ < 10¹¹ cm⁻²eV⁻¹
Interface State Density ($D_{it}$)	4-9 $\times$ 10¹²	cm⁻²eV⁻¹	Extracted via high-low C-V method
Phosphorus Doping ($N_p$) Range	2 $\times$ 10¹⁵ to 6 $\times$ 10¹⁶	cm⁻³	N-type body concentration
Boron Doping ($p^{+}$ layer)	$\sim$ 1 $\times$ 10²⁰	cm⁻³	Heavily doped ohmic contact layer
Gate Oxide Material	Al₂O₃	-	Deposited by ALD
Gate Oxide Thickness	34	nm	Used for MOS capacitors and MOSFETs
Homoepitaxial Substrate	HPHT (111)	-	Semi-insulating SCD
Heteroepitaxial Substrate	Ir/intermediate layer/Si (111)	-	Used for large-area potential
Surface Roughness (RMS)	2.2 to 30.6	nm	Heteroepitaxial diamond surface

Key Methodologies

The fabrication of the inversion-type p-channel diamond MOSFETs relied heavily on precise MPCVD growth and controlled surface termination techniques.

Substrate Preparation:
- Homoepitaxy: HPHT synthetic Ib (111) semi-insulating single-crystal diamond substrates were used.
- Heteroepitaxy: Ir/intermediate layer/Si (111) substrates (10 mm diameter) were used, followed by mechanical polishing to achieve a 104 µm thick freestanding diamond layer.
N-type Body Layer Growth (MPCVD):
- Phosphorus-doped n-type body layer ($\sim$ 10 µm thick) was deposited via Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD).
- Recipe Parameters: Methane concentration 0.4%, Plasma power 3.6 kW, Chamber pressure 150 Torr.
P+-layer Growth (MPCVD):
- A heavily boron-doped p+-layer ($\sim$ 50 nm thick, $\sim$ 1 $\times$ 10²⁰ cm⁻³) was selectively grown using a metal mask.
- Recipe Parameters: Methane concentration 0.2%, Plasma power 1200 W, Chamber pressure 50 Torr.
OH-Termination (Novel Wet Annealing):
- Samples were subjected to water vapor annealing (bubbling N₂ carrier gas through de-ionized water) at 500 °C for 60 min.
- Note: For improved interface quality, this process was applied to H-terminated diamond, rather than O-terminated diamond.
Gate Oxide Deposition:
- 34 nm thick Al₂O₃ film was deposited by Atomic Layer Deposition (ALD) at 300 °C.
Metalization:
- Ti/Pt/Au (30/30/100 nm) electrodes were evaporated to form the gate, drain, and source contacts.
Characterization:
- Electrical properties were measured using a Keithley 4200-SCS parameter analyzer.
- Interface quality was analyzed using high-low Capacitance-Voltage (C-V) and high-temperature Conductance methods, considering surface potential fluctuation.

6CCVD Solutions & Capabilities

The research demonstrates that the path to commercializing diamond MOSFETs hinges on achieving superior material quality, precise doping control, and large-area scalability—all core competencies of 6CCVD.

Applicable Materials

To replicate and advance the high-performance homoepitaxial devices, and to scale the heteroepitaxial devices for commercial use, 6CCVD recommends the following materials:

High-Purity Single Crystal Diamond (SCD): Required for the highest mobility devices (homoepitaxy). 6CCVD offers SCD plates up to 500 µm thick, grown via MPCVD, providing the necessary low defect density platform.
Precisely Doped SCD/PCD: To achieve the required N-type body (Phosphorus doping) and P+-layer (Boron doping) for threshold voltage control, 6CCVD offers custom-doped SCD and PCD films. We guarantee reproducible control of doping concentrations in the 10¹⁵ to 10²⁰ cm⁻³ range.
Large-Area Polycrystalline Diamond (PCD): Essential for commercialization, addressing the size limitations of HPHT substrates. 6CCVD provides large-area PCD wafers up to 125mm in diameter, suitable for scaling the heteroepitaxial approach demonstrated in the paper.
Boron-Doped Diamond (BDD): For highly conductive ohmic contacts (like the p+-layer), 6CCVD provides heavily BDD films (up to 10²¹ cm⁻³) for superior conductivity and low contact resistance.

Customization Potential

The paper highlights several fabrication steps that require specialized material processing, which 6CCVD offers as standard services:

Research Requirement	6CCVD Custom Capability	Benefit to Research
Low Channel Mobility (due to Roughness)	Ultra-Polishing: SCD Ra < 1 nm; Inch-size PCD Ra < 5 nm.	Directly reduces surface roughness scattering, critical for achieving $\mu_{FE}$ > 1000 cm²V⁻¹s⁻¹.
Custom Metalization (Ti/Pt/Au)	In-House Metalization: Deposition of Au, Pt, Pd, Ti, W, and Cu.	Enables rapid prototyping and optimization of gate and ohmic contacts for both homo- and heteroepitaxial devices.
Specific Layer Thicknesses	Custom Thickness Control: SCD/PCD films available from 0.1 µm up to 500 µm.	Allows precise control over the n-type body layer thickness (10 µm used in the paper) and the p+-layer thickness (50 nm).
Large-Area Substrates	PCD Wafers up to 125mm: Custom dimensions and thicknesses available.	Facilitates the transition from small-scale HPHT research to mass-producible, commercially viable devices on large wafers.

Engineering Support

The challenges identified in this research—specifically the high $D_{it}$ and the need for advanced passivation techniques (like the novel OH-termination)—require deep material science expertise.

6CCVD’s in-house PhD engineering team specializes in diamond surface chemistry and interface physics. We can assist researchers and engineers with:

Interface Passivation Optimization: Consulting on surface termination methods (H-termination, O-termination, OH-termination) to minimize $D_{it}$ for Al₂O₃/diamond interfaces.
Doping Profile Management: Designing custom MPCVD recipes to achieve the precise N-type (Phosphorus) doping profiles necessary for stable threshold voltage modulation in inversion-type MOSFETs.
Material Selection for Power Applications: Guiding material choices (SCD vs. PCD) based on specific device requirements, such as high current density or large-area coverage for power switching devices.

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

View Original Abstract

Abstract This article reviews the state of the art in inversion-type p-channel diamond MOSFETs. We successfully developed the world’s first inversion-channel homoepitaxial and heteroepitaxial diamond MOSFETs. We investigated the dependence of phosphorus concentration ( N P ) of the n-type body on field-effect mobility ( μ FE ) and interface state density ( D it ) for the inversion channel homoepitaxial diamond MOSFETs. With regard to the electrical properties of both the homoepitaxial and heteroepitaxial diamond MOSFETs, they suffer from low μ FE and one main reason is high D it . To improve the interface quality, we proposed a novel technique to form OH-termination by using H-diamond followed by wet annealing, instead of the previous OH-termination formed on O-diamond. We made precise interface characterization for diamond MOS capacitors by using the high-low C-V method and the conductance method, providing further insights into the trap properties at Al 2 O 3 /diamond interface, which would be beneficial for performance enhancement of the inversion-type p-channel diamond MOSFETs. Graphic abstract

Tech Support

Original Source

DOI: https://doi.org/10.1557/s43578-021-00317-z