Diamond for High-Power, High-Frequency, and Terahertz Plasma Wave Electronics

At a Glance

Metadata	Details
Publication Date	2024-03-01
Journal	Nanomaterials
Authors	Muhammad Mahmudul Hasan, Chunlei Wang, Nezih Pala, M. S. Shur
Institutions	Rensselaer Polytechnic Institute, Florida International University
Citations	21
Analysis	Full AI Review Included

Executive Summary

This review analyzes the state-of-the-art in diamond electronics, positioning it as a superior material for extreme high-power and high-frequency applications, particularly in the Terahertz (THz) regime.

Unmatched Material Properties: Diamond exhibits the highest combined Figure of Merit (CFOM > 124,000 relative to Si), driven by its ultra-wide bandgap (5.47 eV), exceptional thermal conductivity (up to 2300 W/mK), and high breakdown field (10 MV/cm).
High-Power Device Performance: Diamond Schottky Barrier Diodes (SBDs) and PiN diodes have demonstrated breakdown voltages exceeding 10 kV and 11 kV, respectively, making them ideal for high-voltage power electronics.
RF Performance Benchmarks: H-terminated Field Effect Transistors (H-FETs) have achieved a maximum frequency (f_max) of 120 GHz and a cutoff frequency (f_T) of 70 GHz, with output power densities up to 3.8 W/mm at 1 GHz.
THz and 6G Potential (TeraFETs): Diamond’s long carrier momentum relaxation time facilitates the use of plasma waves in Terahertz Field-Effect Transistors (TeraFETs). P-diamond TeraFETs are predicted to achieve resonant operation at room temperature in the 200-600 GHz range.
Material Challenges: While p-type doping (Boron) and surface transfer doping are mature, challenges persist in achieving scalable substrate size, high lattice quality, and efficient n-type doping (Phosphorus activation energy is 0.6 eV, still deep).
Key Technology Advancement: Surface Transfer Doping (STD) using electron acceptors (like NO₂ or MoO₃) creates a high-mobility 2D Hole Gas (2DHG) channel, circumventing the need for deep bulk doping.

Technical Specifications

Parameter	Value	Unit	Context
Combined Figure of Merit (CFOM)	124,424	N/A	Relative to Silicon (Si = 1)
Thermal Conductivity (Room Temp)	2200	W/mK	Exceptional heat dissipation
Energy Bandgap (E_G)	5.47	eV	Ultra-wide bandgap semiconductor (UWBGS)
Breakdown Field (E_B)	10	MV/cm	Highest among WBG materials
Intrinsic Electron Mobility	7300	cm²/Vs	Measured in ultrapure diamond
Intrinsic Hole Mobility	5300	cm²/Vs	Measured in ultrapure diamond
P-type Dopant Activation Energy	0.37	eV	Boron (B)
N-type Dopant Activation Energy	0.6	eV	Phosphorus (P)
Electron Saturation Velocity	1.5 to 2.7 x 10⁷	cm s^-1	High-frequency operation limit
Lowest Reported Sheet Resistance	719	Ω/□	H-terminated surface, NO₂ acceptor
Lateral SBD Breakdown Voltage	>10	kV	High-power device performance
PiN Diode Breakdown Voltage	11.5	kV	Highest reported blocking voltage
H-FET Output Power Density	3.8	W/mm	At 1 GHz, using ALD Al₂O₃ gate
H-FET Maximum Frequency (f_max)	120	GHz	Polycrystalline diamond, 100 nm gate length
H-FET Cutoff Frequency (f_T)	70	GHz	MISFET configuration, 100 nm gate length
TeraFET Resonant Frequency	200-400	GHz	P-diamond, 80-120 nm channel length
Target Communication Frequency	300	GHz	6G communication systems

Key Methodologies

The development of high-performance diamond devices relies on precise material synthesis and doping techniques:

Diamond Growth Technologies:
- High-Pressure, High-Temperature (HPHT): Primarily used for producing synthetic diamond and highly pure Type IIa substrates. Substrate size is typically limited to less than 1 cm².
- Chemical Vapor Deposition (CVD): Preferred for electronics due to its ability to produce larger substrates with acceptable dislocation density (10²-10⁵ cm^-2).
  - Process Gases: H₂ and CH₄ (Methane is the carbon source).
  - Activation: Microwave Plasma-Assisted CVD (MPCVD) is the established method, providing high-quality, high-purity crystals (Nitrogen concentration less than 5 ppb).
  - Scaling: Techniques like lateral growth and mosaic growth (combining small seeds) are used to increase wafer size (e.g., 40 x 60 mm² mosaics).
P-Type Doping (Boron):
- In Situ CVD Growth: Boron source gases (e.g., Diborane, trimethylboron) are incorporated during CVD growth. This is the most established method.
- Ion Implantation: Highly energized Boron ions are bombarded into the diamond layer, followed by annealing and etching to repair lattice damage and achieve ohmic contact.
- Surface Transfer Doping (STD): Creates a 2D Hole Gas (2DHG) channel near the surface, bypassing bulk doping issues.
  - Mechanism: Hydrogen termination of the diamond surface (H-FET) creates negative electron affinity.
  - Acceptors: Molecular species (Fullerene, F4-TCNQ) or metal oxides (MoO₃, V₂O₅, Al₂O₃) are deposited to act as electron acceptors, transferring charge to the diamond surface.
N-Type Doping (Phosphorus):
- Source Gas: Phosphine (PH₃) is typically used.
- Challenge: Phosphorus has a large covalent bond mismatch with Carbon, making incorporation difficult and resulting in a deep donor activation energy (0.6 eV), leading to low conductivity compared to p-type diamond.
- Co-Doping: Investigating co-doping (e.g., B-P or B-H) to improve lattice structure and conductivity.
High-Frequency Device Fabrication:
- H-FETs: Utilize the high-mobility 2DHG channel created by H-termination and surface transfer doping.
- Gate Dielectrics: High-k materials like Al₂O₃ (often deposited via Atomic Layer Deposition, ALD) are used for passivation and gate insulation to improve stability and reduce gate leakage current.
- TeraFET Design: Devices are designed with asymmetric boundary conditions (shorted source-gate side) and short channel lengths (down to 100 nm) to promote plasma wave oscillation for THz detection and emission.

Commercial Applications

Diamond’s unique combination of electronic and thermal properties targets several high-demand engineering sectors:

6G Communications: Realization of compact, room-temperature THz sources and detectors (TeraFETs) operating in the 240-600 GHz atmospheric window.
High-Power Electronics: Fabrication of high-voltage switching devices (SBDs, PiN diodes) for renewable energy transport, distribution, and power conversion systems, offering superior efficiency and thermal management compared to SiC and GaN.
Extreme Environment Electronics: Devices capable of withstanding high temperatures (melting point 3550 °C) and high radiation environments (high radiation hardness).
Radio Frequency (RF) Devices: High-frequency FETs (f_max up to 120 GHz) for advanced radar and wireless systems.
Advanced Sensing and Imaging: THz spectroscopy, security systems, medical imaging, and bio/chemical sensing utilizing compact THz plasmonic detectors.
VLSI Testing: High-speed testing of monolithic integrated circuits in the sub-THz and THz regions.
IoT Networking: Potential for high-speed, low-power components in complex networking architectures.

View Original Abstract

High thermal conductivity and a high breakdown field make diamond a promising candidate for high-power and high-temperature semiconductor devices. Diamond also has a higher radiation hardness than silicon. Recent studies show that diamond has exceptionally large electron and hole momentum relaxation times, facilitating compact THz and sub-THz plasmonic sources and detectors working at room temperature and elevated temperatures. The plasmonic resonance quality factor in diamond TeraFETs could be larger than unity for the 240-600 GHz atmospheric window, which could make them viable for 6G communications applications. This paper reviews the potential and challenges of diamond technology, showing that diamond might augment silicon for high-power and high-frequency compact devices with special advantages for extreme environments and high-frequency applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano14050460

References

2005 - THz imaging and sensing for security applications—Explosives, weapons and drugs [Crossref]
2019 - Sub-terahertz testing of millimeter wave monolithic and very large scale integrated circuits [Crossref]
2017 - Terahertz beam testing of millimeter wave monolithic integrated circuits [Crossref]