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6CCVD Research

Diamond and III-nitride wide-bandgap semiconductors - a research journey

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-09-05
JournalFunctional Diamond
AuthorsYasuo Koide
InstitutionsMeijo University
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This review details a research journey focused on advancing wide-bandgap semiconductors (III-nitrides and Diamond) for high-performance electronic and optical devices.

  • AlGaN Growth Mastery: Achieved the world’s first successful growth of high-quality AlxGa1-xN (x up to 0.4) using Metal-Organic Vapor Phase Epitaxy (MOVPE), establishing the critical role of low-temperature AlN buffer layers and high gas flow rates for composition control.
  • Contact Material Guidelines: Developed essential guidelines for low-resistance Ohmic contacts, including carbide-based materials (TiC, MoC) for p-diamond and the necessity of oxygen annealing for p-GaN (reducing specific contact resistance to 2-3 x 10-3 Ω-cm2).
  • Thermally Stable DUV Detectors: Developed solar-blind Deep Ultraviolet (DUV) photodetectors based on diamond, demonstrating thermal stability and achieving a visible-blind ratio of nearly 108.
  • High-Performance Diamond MOSFETs: Demonstrated diamond Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) utilizing the H-terminated surface conductive layer and high-k dielectrics (e.g., ZrO2/Al2O3).
  • Logic Circuit Validation: Successfully fabricated the first diamond logic inverter circuit using threshold-controlled MOSFETs, validating diamond’s potential for high-power integrated circuits.
  • Extreme-k Dielectrics: Investigated extreme-k dielectrics (k up to 306) for diamond MOS gates to achieve high carrier density (greater than 1x1014 cm-2) and improve breakdown voltage stability.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
AlGaN Bandgap Bowing Parameter (b)1.0 ± 0.3eVFundamental physical value for AlGaN/GaN design
AlGaN MOVPE Growth Temperature1020 to 1120°CDirect growth temperature range
AlN Buffer Layer Growth Temperature~800°CUsed to improve crystalline quality
p-GaN Specific Contact Resistance (ρc)2 to 3 x 10-3Ω-cm2Ni/Au contact after annealing at 500 °C in N2/O2
p-GaN SBH Reduction Targetless than 0.7eVRequired for low-resistance Ohmic contact
Diamond DUV Detection Wavelength190 to 260nmSolar-blind photodetector range
Diamond Photoconductor Visible-Blind RatioNearly 108N/ADiscrimination ratio (210 nm vs. visible light)
Diamond MOSFET Max Drain Current (IDSmax)-224.1mA-mm-1SD-ZrO2/ALD-Al2O3 MOSFET (without channel resistance)
Diamond MOSFET Effective Mobility (”eff)217.5 ± 0.5cm2-V-1-s-1SD-ZrO2/ALD-Al2O3 MOSFET
Diamond MOSFET On-Resistance (RON)29.7Ω-mmSD-ZrO2/ALD-Al2O3 MOSFET (without channel resistance)
Extreme-k Dielectric Constant (k)306N/AALD-AlOx/TiOy nanolaminate layer

Key Methodologies

Section titled “Key Methodologies”
  1. Custom MOVPE Reactor Design: Utilized a Type-B reactor configuration for AlGaN growth, feeding mixed gases (TMG, TMA, NH3, H2) through a delivery tube at a high velocity (110 cm/s) to suppress parasitic gas-phase reactions and achieve compositional control.
  2. AlN Buffer Layer Technique: Employed a low-temperature (~800 °C) AlN buffer layer deposition prior to AlGaN growth to minimize orientation fluctuation and improve the smoothness and uniformity of the epitaxial layer.
  3. Gas-Source Molecular Beam Epitaxy (GSMBE): Used GSMBE combined with in-situ Reflection High-Energy Electron Diffraction (RHEED) to study the growth mechanism of Si1-xGex alloys, focusing on dynamic surface adsorption and desorption processes.
  4. Carbide-Based Ohmic Contacts for Diamond: Developed a guideline to select contact metals (Ti, Mo, Cr) that undergo metallurgical reaction with diamond at elevated temperatures (greater than 500 °C) to form stable carbide interfacial layers (TiC, MoC, Cr2C3).
  5. Oxygen Ambient Annealing for p-GaN: Demonstrated that annealing Ni/Au contacts on p-GaN in a partial oxygen ambient (N2/O2) at 500 °C effectively reduces contact resistance by removing hydrogen atoms bonded to Mg acceptors, thereby increasing hole concentration.
  6. High-k/Extreme-k Gate Dielectrics: Fabricated diamond MOSFETs using bilayer gate dielectrics (e.g., SD-ZrO2/ALD-Al2O3) deposited via sputtering (SD) and Atomic Layer Deposition (ALD) to control high-density hole carriers in the H-terminated diamond channel.

Commercial Applications

Section titled “Commercial Applications”
  • High-Power and High-Temperature Electronics: Diamond’s superior thermal conductivity, high breakdown field, and chemical stability make it ideal for power MOSFETs, power integrated circuits, and devices operating in extreme environments (e.g., aerospace, industrial control).
  • Advanced Communications (5G/6G): III-nitride (GaN) High-Electron Mobility Transistors (HEMTs) are essential for high-frequency applications (28 GHz to 330 GHz). The hybridization of GaN with diamond substrates is critical for thermal management in high-power RF amplifiers.
  • Deep Ultraviolet (DUV) Technology: Thermally stable, solar-blind DUV photodetectors are used in flame sensors, industrial process monitoring, and military applications requiring detection in the 190-260 nm range, unaffected by visible light.
  • Energy-Efficient Lighting: The foundational research on AlGaN growth enabled the commercialization of high-brightness blue and UV Light-Emitting Diodes (LEDs) and Laser Diodes (LDs).
  • High-Frequency Integrated Circuits: SiGe-based semiconductors are used in ultra-high frequency electronic devices, leveraging precise thin-film growth techniques developed in this research.
  • Radiation-Hardened Computing: Diamond logic inverter circuits demonstrate the potential for robust, radiation-hardened computing systems capable of functioning reliably in harsh environments where silicon devices fail.
View Original Abstract

My research progress to date is reviewed by focusing on III-nitride and diamond semiconductors within the scope of my limited experience. I have developed high-quality AlxGa1-xN epitaxial layers, Ohmic contact materials for GaN and diamond, and diamond optical and electronic devices. While my research themes have changed at each university and national laboratory, I have been involved in semiconductor crystal growth, electrode formation, processing, and device development. I believe that my broad experience in materials research will lead to new discoveries in a variety of semiconductor fields.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2005 - Thermally-stable visible-blind diamond photodiode using WC schottky contact

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