Reliable Ohmic Contact Properties for Ni/Hydrogen-Terminated Diamond at Annealing Temperature up to 900 °C

At a Glance

Metadata	Details
Publication Date	2021-04-17
Journal	Coatings
Authors	Xiaolu Yuan, Jiangwei Liu, Jinlong Liu, Junjun Wei, Bo Da
Institutions	University of Science and Technology Beijing, National Institute for Materials Science
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Temperature Ohmic Contacts on H-Diamond

Executive Summary

This research successfully demonstrates the fabrication of highly reliable, thermal-stable ohmic contacts on hydrogen-terminated diamond (H-diamond) using Nickel (Ni) electrodes, achieving performance critical for next-generation high-power and high-temperature electronics.

Thermal Stability Benchmark: Stable ohmic contact properties were maintained after rapid thermal annealing (RTA) up to 900 °C in an Argon atmosphere, significantly exceeding the stability limits of many conventional diamond metallization schemes (typically <700 °C).
Optimized Contact Resistance: The specific contact resistance ($\rho_c$) was dramatically reduced from Schottky behavior (as-received) to an optimized value of 6.0 x 10^-5 Ω·cm² after 900 °C annealing.
Mechanism Validation: The transition from Schottky to Ohmic behavior is driven by the solid-solution reaction between Ni and C, leading to the formation of Ni-related carbides at the interface, confirmed via TEM and EDS analysis.
Material Foundation: The experiment relied on high-quality, Ib-type (100) single-crystal diamond (SCD) substrates for the subsequent MPCVD growth of the 150 nm H-diamond epitaxial layer.
Application Relevance: This breakthrough validates the Ni/H-diamond system as a robust solution for diamond-based field-effect transistors (FETs) and other devices requiring operation in extreme thermal environments.

Technical Specifications

The following hard data points were extracted from the experimental results, focusing on the optimized 900 °C annealing condition.

Parameter	Value	Unit	Context
Substrate Material	Ib-type (100)	N/A	Single-Crystal Diamond (SCD)
H-Diamond Epitaxial Thickness	150	nm	Grown via MPCVD
Ni Contact Thickness	100	nm	Deposited via e-beam evaporation
Optimized Annealing Temperature	900	°C	Rapid Thermal Annealing (RTA) in Ar
Lowest Specific Contact Resistance ($\rho_c$)	6.0 x 10^-5	Ω·cm²	Achieved after 900 °C annealing
Contact Resistance ($R_C$) at 900 °C	19.0	Ω	Calculated from TLM data
Surface Sheet Resistance ($R_S$) at 900 °C	60.6	kΩ	Increased due to high-temperature treatment
Transfer Length ($L_T$) at 900 °C	0.1	µm	Critical dimension for contact effectiveness
Transition Temperature (Schottky to Ohmic)	500	°C	Minimum temperature required for Ohmic formation
Diamond Energy Bandgap	5.5	eV	Intrinsic property of diamond

Key Methodologies

The following ordered list outlines the critical steps and recipe parameters used in the fabrication of the Ni/H-diamond contacts.

Substrate Preparation: Ib-type (100) SCD substrates were chemically cleaned by boiling in a mixed H₂SO₄ and HNO₃ solution at 300 °C for 3 hours.
H-Diamond Epitaxial Growth (MPCVD): A 150 nm H-diamond layer was grown using a Microwave Plasma-Enhanced Chemical Vapor Deposition system under the following conditions:
- Deposition Temperature: 900-940 °C
- Chamber Pressure: 80 Torr
- Gas Flow Rates: CH₄ (0.5 sccm) / H₂ (500 sccm)
Mesa Structure Formation: Capacitively Coupled Plasma Reactive-Ion Etching (RIE) was used with O₂ plasma (50 W power, 100 sccm flow, 90 s etch time) to define the active device area.
TLM Patterning and Metalization: Transmission Line Model (TLM) patterns were defined using mask-less lithography. A 100 nm thick Nickel (Ni) layer was deposited via e-beam evaporation under a high vacuum (~10^-5 Pa).
High-Temperature Annealing: Samples underwent Rapid Thermal Annealing (RTA) in an inert Argon (Ar) atmosphere at sequential temperatures (300, 500, 700, and 900 °C) for 10 minutes at each step.
Post-Annealing Surface Recovery: Samples were exposed to ambient air for >10 hours post-annealing to promote the formation of a negatively adsorbed layer, essential for regaining high surface conductivity.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, customized diamond materials and precise metalization techniques to achieve high-performance, thermal-stable electronic devices. 6CCVD is uniquely positioned to supply the foundational materials and processing capabilities required to replicate and advance this work.

Research Requirement	6CCVD Solution & Capability	Technical Advantage for High-Temperature Devices
High-Purity Substrates (Ib-type (100) SCD)	Optical Grade Single Crystal Diamond (SCD)	SCD wafers up to 500 µm thick, ensuring ultra-low defect density and optimal crystalline orientation (e.g., (100) or (111)) for repeatable epitaxial growth.
Custom Layer Thickness (150 nm H-diamond)	Precision MPCVD Growth	We provide SCD and Polycrystalline Diamond (PCD) layers with thickness control from 0.1 µm up to 500 µm, tailored specifically for surface conductivity applications.
Metalization Requirements (Ni, Ti key-patterns)	Custom Metalization Services	6CCVD offers in-house deposition of carbide-forming metals (Ni, W, Ti) and noble metals (Au, Pt, Pd) via e-beam or sputtering, crucial for forming stable ohmic contacts up to 900 °C.
Large Area Processing (Scalability)	Large Format Wafers	While the paper used small TLM patterns, 6CCVD can supply PCD plates and wafers up to 125 mm in diameter, enabling scalable production of high-temperature devices.
Surface Quality (TLM patterning)	Ultra-Low Roughness Polishing	Our SCD polishing achieves Ra < 1 nm, providing the atomically flat surface necessary for high-fidelity lithography, precise contact alignment, and minimizing interface scattering.
Engineering Consultation (Interface Optimization)	In-House PhD Engineering Support	6CCVD’s team specializes in material selection and surface termination (H-termination, O-termination, BDD) to optimize contact formation and thermal stability for high-power applications.

Applicable Materials

To replicate or extend this research into commercial high-temperature electronics, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required as the foundation for the high-quality epitaxial H-diamond layer. Our SCD ensures the necessary low defect density and precise (100) orientation used in the study.
Custom Metalized SCD Wafers: We can deliver SCD wafers pre-metalized with custom stacks (e.g., Ti/Ni/Au or Ni only) ready for high-temperature RTA processing, streamlining the customer’s fabrication workflow.

Customization Potential

The success of this research hinges on precise material dimensions and interface engineering. 6CCVD offers:

Custom Dimensions: Supply of SCD substrates cut to specific sizes required for RTA systems or custom device layouts.
Advanced Metal Stacks: Beyond the Ni contact used here, 6CCVD can engineer complex metal stacks (e.g., Ti/Pt/Au) known for high-temperature stability, providing alternatives for comparative studies.
Global Logistics: Global shipping is available (DDU default, DDP available) to ensure rapid delivery of specialized diamond materials worldwide.

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

View Original Abstract

Ohmic contact with high thermal stability is essential to promote hydrogen-terminated diamond (H-diamond) electronic devices for high-temperature applications. Here, the ohmic contact characteristics of Ni/H-diamond at annealing temperatures up to 900 °C are investigated. The measured current-voltage curves and deduced specific contact resistance (ρC) are used to evaluate the quality of the contact properties. Schottky contacts are formed for the as-received and 300 °C-annealed Ni/H-diamonds. When the annealing temperature is increased to 500 °C, the ohmic contact properties are formed with the ρC of 1.5 × 10−3 Ω·cm2 for the Ni/H-diamond. As the annealing temperature rises to 900 °C, the ρC is determined to be as low as 6.0 × 10−5 Ω·cm2. It is believed that the formation of Ni-related carbides at the Ni/H-diamond interface promotes the decrease in ρC. The Ni metal is extremely promising to be used as the ohmic contact electrode for the H-diamond-based electronic devices at temperature up to 900 °C.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings11040470

References

2019 - 3.8W/mm RF power density for ALD Al2O3-based two-dimensional hole gas diamond mosfet operating at saturation velocity [Crossref]
2020 - High-temperature diamond detector for neutron generator output monitoring in well logging applications [Crossref]
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2019 - Operations of hydrogenated diamond metal-oxide-semiconductor field-effect transistors after annealing at 500 °C [Crossref]