Hydrogen-Terminated Single Crystal Diamond MOSFET with a Bilayer Dielectric of Gd2O3/Al2O3

At a Glance

Metadata	Details
Publication Date	2023-05-08
Journal	Crystals
Authors	Xiaoyong Lv, Wei Wang, Yanfeng Wang, Genqiang Chen, Shi He
Institutions	Xi’an Jiaotong University
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance H-Diamond MOSFETs

Executive Summary

This technical analysis focuses on the successful fabrication and characterization of a high-performance, hydrogen-terminated single-crystal diamond (H-diamond) MOSFET utilizing a novel Gd₂O₃/Al₂O₃ bilayer dielectric stack. This research validates the use of high-k dielectrics on diamond for next-generation power and high-frequency electronics.

Core Achievement: Successful integration of a high-k Gd₂O₃ (k=24.8) layer via magnetron sputtering (SD) atop an ALD-Al₂O₃ buffer layer on a single-crystal H-diamond substrate.
High Current Density: The device achieved a maximum drain current density (I_Dmax) of 15.3 mA/mm, demonstrating excellent current handling capability for p-type MOSFETs.
High Mobility: An effective carrier mobility (µ_eff) of 182.1 cm²/Vs was achieved, confirming the quality of the 2DHG channel interface.
Excellent Switching: The device exhibited a high ON/OFF ratio of 5 x 10⁸, suitable for practical switching applications.
Material Stability: The bilayer dielectric stack demonstrated high stability, resulting in a very low gate leakage current density (< 1 x 10⁻⁷ A/cm²).
6CCVD Value Proposition: 6CCVD provides the necessary high-quality, ultra-pure Single Crystal Diamond (SCD) substrates and custom epitaxial layers required to replicate and scale this advanced device architecture.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Material	SCD (001)	N/A	HPHT synthesized, 3 x 3 x 0.5 mm³
Epitaxial Layer Thickness	200	nm	Undoped SCD grown via MPCVD
Maximum Drain Current (I_Dmax)	15.3	mA/mm	At V_DS = -20 V, V_GS = 10 V
Effective Carrier Mobility (µ_eff)	182.1	cm²/Vs	Measured at V_GS = 1 V
ON/OFF Ratio	5 x 10⁸	N/A	High switching performance
Threshold Voltage (V_TH)	1.12	V	Extracted from transfer characteristics
Max Transconductance (g_m,max)	2.01	mS/mm	At V_GS = -10.63 V
Subthreshold Swing (SS)	315	mV/dec	Indicates switching speed characteristics
Gd₂O₃ Dielectric Constant (k)	24.8	N/A	High-k layer via Magnetron Sputtering
Al₂O₃ Dielectric Constant (k)	4.9	N/A	Buffer layer via ALD
Total Dielectric Constant (k)	11.9	N/A	Overall bilayer stack
Gate Leakage Current Density (J)	< 1 x 10⁻⁷	A/cm²	Indicates excellent dielectric integrity
Trapped Charge Density (Q_t)	1.08 x 10¹¹	cm⁻²	Calculated from C-V hysteresis

Key Methodologies

The device fabrication relies heavily on high-quality diamond epitaxy and precise thin-film deposition techniques, areas where 6CCVD offers specialized material solutions.

Substrate Preparation: A 3 x 3 x 0.5 mm³ HPHT (001) Single Crystal Diamond (SCD) substrate was used, followed by rigorous acid cleaning (H₂SO₄:HNO₃ at 250 °C).
Epitaxial Growth: A 200 nm undoped SCD layer was grown on the HPHT substrate using a Microwave Plasma CVD (MPCVD) system.
2DHG Formation: The methane flow was set to zero, and the sample was treated with hydrogen plasma to form the crucial Hydrogen-Terminated (H-diamond) surface, generating the Two-Dimensional Hole Gas (2DHG).
Source/Drain Metalization: Traditional photolithography was used, followed by Electron Beam (EB) deposition of a 150 nm Au film to form the source and drain electrodes (L_sp = 20 µm).
Dielectric Buffer Layer (Al₂O₃): A 20 nm Al₂O₃ layer was deposited using Atomic Layer Deposition (ALD). The process involved two steps: 5 nm at 80 °C and 15 nm at 250 °C, using water vapor and TMA precursors.
High-k Dielectric Layer (Gd₂O₃): A 52.3 nm Gd₂O₃ layer was deposited via Magnetron Sputtering Deposition (SD) at Room Temperature (RT). Deposition parameters were 0.5 Pa pressure, 75 W power, and 30 minutes time.
Gate Electrode: A 150 nm Al electrode was deposited via EB deposition (L_G = 20 µm, W_G = 100 µm).

6CCVD Solutions & Capabilities

This research demonstrates the critical role of high-quality SCD material and precise interface engineering in achieving high-performance diamond MOSFETs. 6CCVD is uniquely positioned to supply the foundational materials and customization services required to advance this technology.

Applicable Materials

To replicate or extend this high-performance H-diamond MOSFET research, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required for the high-purity, low-defect (001) substrate and subsequent epitaxial growth. 6CCVD provides SCD substrates up to 10 mm thick.
Custom Undoped Epitaxial Layers: 6CCVD specializes in MPCVD growth, allowing precise control over the 200 nm undoped SCD layer thickness and purity, which is essential for consistent 2DHG formation and device performance.
Hydrogen Termination Support: While the H-termination process is typically performed post-delivery, 6CCVD ensures the as-grown SCD surface quality is optimized for subsequent plasma treatment and 2DHG stability.

Customization Potential

The complexity of this bilayer dielectric device requires highly specific material dimensions and metal contacts, capabilities that 6CCVD offers as standard services:

Research Requirement	6CCVD Customization Capability	Technical Advantage
Substrate Size: 3 x 3 mm³	Custom dimensions available, including plates/wafers up to 125 mm (PCD) and large-area SCD.	Enables scaling from R&D prototypes to commercial wafer sizes.
Epitaxy Thickness: 200 nm	Precise thickness control for SCD epitaxy from 0.1 µm to 500 µm.	Guarantees exact layer specifications needed for optimized 2DHG channel depth.
Metalization: Au (Source/Drain), Al (Gate)	Internal metalization services including Au, Pt, Pd, Ti, W, and Cu.	Allows for rapid prototyping and integration of complex multi-layer contact schemes (e.g., Ti/Au ohmic contacts).
Surface Quality: Low defect interface	Polishing capability to achieve surface roughness Ra < 1 nm (SCD).	Minimizes interfacial defects that contribute to high trapped charge density (Q_t) and subthreshold swing (SS).

Engineering Support

The successful integration of high-k dielectrics like Gd₂O₃ (k=24.8) and Al₂O₃ (k=4.9) is highly sensitive to the H-diamond surface chemistry. 6CCVD’s in-house PhD team offers specialized consultation to address these interface challenges:

Interface Optimization: Assistance in selecting the optimal SCD surface orientation and termination (H-terminated vs. O-terminated) based on the specific dielectric stack and target application (e.g., high-power switching or high-frequency communication).
Process Integration: Guidance on material compatibility for ALD/SD processes to minimize plasma damage and reduce trapped charge densities, which directly impacts mobility and SS.
Advanced Device Projects: 6CCVD supports similar projects targeting ultra-wide bandgap (UWBG) semiconductor devices, including high-power MOSFETs and radiation sensors.

Call to Action: For custom specifications or material consultation regarding high-performance H-diamond MOSFETs or other UWBG applications, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this paper, two dielectric layers of Al2O3 and Gd2O3 were prepared by an atomic layer deposition (ALD) and magnetron sputtering deposition (SD), respectively. Based on this, a metal-oxide-semiconductor field-effect transistor (MOSFET) was successfully prepared on a hydrogen-terminated single-crystal diamond (H-diamond), and its related properties were studied. The results showed that this device had typical p-type channel MOSFET output and transfer characteristics. In addition, the maximum current was 15.3 mA/mm, and the dielectric constant of Gd2O3 was 24.8. The effective mobility of MOSFET with Gd2O3/Al2O3 was evaluated to be 182.1 cm2/Vs. To the best of our knowledge, the bilayer dielectric of Gd2O3/Al2O3 was first used in a hydrogen-terminated diamond MOSFET and had the potential for application.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst13050783

References

2021 - 345-MW/cm2 2608-V NO2 p-type Doped Diamond MOSFETs with an Al2O3 Passivation Overlayer on Heteroepitaxial Diamond [Crossref]
2018 - 3.8 W/mm RF Power Density for ALD Al2O3-Based Two-Dimensional Hole Gas Diamond MOSFET Operating at Saturation Velocity [Crossref]
2020 - Normally off hydrogen-terminated diamond field-effect transistor with Ti/TiOx gate materials [Crossref]
2022 - Leakage current reduction of normally off hydrogen-terminated diamond field effect transistor utilizing dual-barrier Schottky gate [Crossref]
2022 - Large VTH of Normally-off Field Effect Transistor with Yttrium Gate Material Directly Deposited on Hydrogen-Terminated Diamond [Crossref]
1988 - Critical evaluation of the status of the areas for future research regarding the wide band gap semiconductors diamond, gallium nitride and silicon carbide [Crossref]
2020 - Oxidized Si terminated diamond and its MOSFET operation with SiO2 gate insulator [Crossref]
2016 - Diamond based field-effect transistors with SiNx and ZrO2 double dielectric layers [Crossref]
2023 - High Performance of Normally-on and Normally-off Devices with Highly Boron-Doped Source and Drain on H-Terminated Polycrystalline Diamond [Crossref]
2012 - Development of AlN/diamond heterojunction field effect transistors [Crossref]