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6CCVD Research

The Influence of Process Parameters on Hydrogen-Terminated Diamond and the Enhancement of Carrier Mobility

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-12-30
JournalMaterials
AuthorsXingqiao Chen, Mingyang Yang, Yuanyuan Mu, Chengye Yang, Zhenglin Jia
InstitutionsUniversity of Chinese Academy of Sciences, Hefei National Center for Physical Sciences at Nanoscale
Citations1
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research successfully optimized process parameters for Microwave Plasma Chemical Vapor Deposition (MPCVD) to produce Hydrogen-Terminated Diamond (H-Diamond) films exhibiting significantly enhanced carrier mobility for semiconductor applications.

  • Record Carrier Mobility: Achieved a peak carrier mobility of 395 cm2/(Vs), dramatically surpassing the typical range of 50-200 cm2/(Vs) reported for H-diamond, validating its potential for high-performance devices.
  • Optimized Growth Recipe: The highest quality film was obtained using 4% CH4 concentration during homoepitaxial growth, resulting in the lowest crystal defects (Raman FWHM of 2.21 cm-1).
  • Surface Treatment Optimization: Post-growth hydrogen plasma etching was optimized at 900 °C for 30 minutes, which effectively smoothed the surface (RMS roughness of 1.48 nm) and reduced defects, maximizing carrier transport.
  • High Surface Quality: The optimal film exhibited extremely low surface roughness (1.26 nm RMS) and low sheet resistance (7.82 kΩ/square) at a carrier concentration of 2.03 x 1012/cm2.
  • Mechanism of Enhancement: Homoepitaxial growth minimizes the influence of non-diamond (sp2) phases and impurities, while optimized H-plasma treatment ensures a stable C-H bond termination, crucial for the formation of the P-type Two-Dimensional Hole Gas (2DHG).
  • Material Selection Reference: The findings provide a critical material choice reference for developing next-generation high-power, high-frequency, and high-temperature electronic devices.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Peak Carrier Mobility395cm2/(Vs)Optimal H-diamond (4% CH4, 30 min H-etch)
Sheet Resistance (Minimum)7.82kΩ/squareCorresponds to peak mobility sample
Carrier Concentration2.03 x 1012/cm2Corresponds to peak mobility sample
Optimal CH4 Concentration4%For highest crystallinity and lowest roughness
Minimum Surface Roughness (RMS)1.26nmAchieved at 4% CH4 concentration
Raman FWHM (Minimum)2.21cm-1Indicates highest crystal quality (at 4% CH4)
Diamond Band Gap5.5eVIntrinsic property of diamond
Intrinsic Hole Mobility (Theoretical)3800cm2/(Vs)Highest reported intrinsic value
Optimal H-Plasma Etch Time30minPost-growth treatment for surface smoothing
Optimal H-Plasma Etch Temperature900°CFor direct substrate treatment
CVD Growth Temperature Range950-980°CHomoepitaxial growth conditions
CVD Growth Pressure Range13-15kPaHomoepitaxial growth conditions

Key Methodologies

Section titled “Key Methodologies”

The hydrogen-terminated diamond films were prepared using Microwave Plasma Chemical Vapor Deposition (MPCVD) on single-crystal diamond substrates, focusing on three variable parameters: CH4 concentration, hydrogen etching time, and hydrogen plasma temperature.

  1. Substrate Pre-treatment:
    • CVD single-crystal diamond (100) substrates (5 mm x 5 mm x 0.5 mm) were acid-washed using piranha solution (H2O2:H2SO4 = 3:7) for 4 hours.
    • Substrates were subsequently cleaned ultrasonically in deionized water and anhydrous ethanol.
  2. In-situ Hydrogen Pre-Etching:
    • Samples were placed in the MPCVD chamber and vacuumed to 0.5 Pa.
    • Hydrogen plasma pre-etching was performed for 10 minutes at approximately 900 °C to remove surface impurities and non-diamond phases, improving epitaxial purity.
  3. Homoepitaxial Growth (CH4 Concentration Study):
    • Growth was carried out for 8 hours at 950 °C-980 °C, 4200 W-4600 W, and 13 kPa-15 kPa.
    • CH4 concentration was systematically varied from 1% to 5% to determine the optimal growth quality (found to be 4%).
  4. Post-Growth Hydrogen Etching (Time Study):
    • After growth (using 3% CH4 samples), CH4 was turned off, and hydrogen etching was performed at 900 °C.
    • Etching time was varied (15 min, 30 min, 45 min) to optimize surface roughness and electrical properties.
  5. Direct Hydrogen Plasma Treatment (Temperature Study):
    • Separate samples were treated directly with H-plasma for 30 minutes, varying the temperature from 600 °C to 1000 °C to assess the effect on carrier concentration and mobility.
  6. Characterization:
    • Crystal quality was assessed by Raman spectroscopy (FWHM).
    • Surface roughness and morphology were measured by Atomic Force Microscopy (AFM).
    • Surface chemical bonding (C-H, C-O, sp2) was analyzed by X-ray Photoelectron Spectroscopy (XPS).
    • Electrical properties (mobility, concentration, sheet resistance) were tested using the Hall effect system.

Commercial Applications

Section titled “Commercial Applications”

The development of high-mobility hydrogen-terminated diamond films significantly enhances the viability of diamond as a foundational material for advanced semiconductor devices, leveraging its intrinsic ultra-wide band gap properties.

  • High-Frequency (RF) Devices:
    • The high carrier mobility (395 cm2/(Vs)) is crucial for fast switching speeds in high-frequency Field-Effect Transistors (FETs) and High Electron Mobility Transistors (HEMTs).
    • The stable 2DHG conductive channel formed by H-termination is the basis for diamond-based RF power amplifiers.
  • High-Power Electronics:
    • Diamond’s exceptional breakdown electric field (>1 MV/mm) combined with enhanced carrier transport enables the creation of highly efficient power switching devices (e.g., diodes, MOSFETs) for electric vehicles, smart grids, and industrial power supplies.
  • Extreme Environment Electronics:
    • The material’s high thermal conductivity (2200 W/(mK)) and wide band gap ensure reliable operation in high-temperature and high-radiation environments, such as aerospace, deep-well drilling, and nuclear facilities.
  • Advanced Substrate Technology:
    • The ability to grow high-quality, smooth homoepitaxial layers (RMS < 2 nm) provides superior substrates for subsequent device fabrication, minimizing interface scattering and maximizing device yield.
View Original Abstract

With the development of diamond technology, its application in the field of electronics has become a new research hotspot. Hydrogen-terminated diamond has the electrical properties of P-type conduction due to the formation of two-dimensional hole gas (2DHG) on its surface. However, due to various scattering mechanisms on the surface, its carrier mobility is limited to 50-200 cm2/(Vs). In this paper, the effects of process parameters (temperature, CH4 concentration, time) on the electrical properties of hydrogen-terminated diamond were studied by microwave plasma chemical vapor deposition (CVD) technology, and hydrogen-terminated diamond with a high carrier mobility was obtained. The results show that homoepitaxial growth of a diamond film on a diamond substrate can improve the carrier mobility. Hydrogen-terminated diamond with a high carrier mobility and low sheet resistance can be obtained by homoepitaxial growth of a high-quality diamond film on a diamond substrate with 4% CH4 concentration and hydrogen plasma treatment at 900 ℃ for 30 min. When the carrier concentration is 2.03 × 1012/cm2, the carrier mobility is 395 cm2/(Vs), and the sheet resistance is 7.82 kΩ/square, which greatly improves the electrical properties of hydrogen-terminated diamond. It can enhance the transmission characteristics of carriers in the conductive channel, and is expected to become a potential material for application in devices, providing a material choice for its application in the field of semiconductor devices.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2020 - Diamond semiconductor performances in power electronics applications [Crossref]
  2. 2023 - Superconductivity at 117 K inH-doped diamond [Crossref]
  3. 2020 - Effects of hydrogen termination of CVD diamond layers [Crossref]
  4. 2021 - Surface transfer doping of diamond: A review [Crossref]
  5. 2013 - Electrical properties of the high quality boron-doped synthetic single-crystal diamonds grown by the temperature gradient method [Crossref]
  6. 2023 - Temperature dependence of two-dimensional hole gas on hydrogen-terminated diamond surface [Crossref]
  7. 2023 - Fabrication of hydroxyl terminateddiamond by high-voltage hydroxide ion treatments [Crossref]
  8. 2024 - Surface transfer doping of hydrogen-terminated diamond probed by shallow nitrogen-vacancy centers [Crossref]
  9. 2018 - Mobility of two-dimen-sional hole gas in H-terminated diamond [Crossref]
  10. 2020 - Investigation of charge carrier trapping in H-terminated diamond devices [Crossref]

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