同軸型アークプラズマ成膜法によるリンドープ単結晶ダイヤモンド上へのナノカーボンオーミックコンタクトの形成

概要

九州大学学術情報リポジトリ
Kyushu University Institutional Repository

Formation of Nanocarbon Ohmic Contacts on
Phosphorous-Doped Single crystalline Diamond by
Coaxial Arc Plasma Deposition
スリーナット マイロ ワラピル

https://hdl.handle.net/2324/6787639
出版情報：Kyushu University, 2022, 博士（学術）, 課程博士
バージョン：
権利関係：Public access to the fulltext file is restricted for unavoidable reason (3)

（様式３）Form 3

氏

名

：Sreenath Mylo Valappil

Name

論文名

： Formation of Nanocarbon Ohmic Contacts on Phosphorous-Doped Single crystalline

Diamond by Coaxial Arc Plasma Deposition
（同軸型アークプラズマ成膜法によるリンドープ単結晶ダイヤモンド上へのナノカーボンオーミッ
クコンタクトの形成）
Title

区

分

：甲

Category

論

文 内 容 の 要
Thesis Summary

旨

The physical properties of diamond have received great attention in recent years to realize
advanced devices. Their large breakdown field (~10 MV cm-1), huge carrier mobilities,
exceptional thermal conductivity (22 W cm-1 K-1), and the wide band gap (5.4 eV) had already
been intensively studied and applied in various devices in the areas of power electronics,
quantum sensing, hard coating, and others. The recent technological advances in efficient p and
n-type doping of the diamond have improved the device properties and their controllability. The
attainment of advanced diamond-based devices is interrelated with the fabrication of practical
ohmic contacts to semiconducting diamond.
This doctoral thesis focuses on fabricating efficient nanocarbon ohmic contacts to phosphorusdoped n-type and boron-doped p-type semiconducting diamonds through the coaxial arc plasma
deposition method and their characterization as compared with conventional Ti-based ohmic
contacts. The accurate extraction of the specific contact resistance is realized through the circular
transmission line model theory. The nanocarbon ohmic contacts exhibited less specific contact
resistance and interfacial potential drop when compared with the conventional Ti ohmic
contacts.
In addition to the low contact resistance, the ideal ohmic electrode is preferable to have good
mechanical adhesion and corrosion resistance for device applications. The contact behavior of
n-type diamond/nanocarbon in an extremely corrosive environment exhibited excellent
corrosion resistance and mechanical adhesion over conventional Ti-based contacts. Moreover,
this study deeply explored the structural configuration of the alternative nanocarbon ohmic
electrodes on the phosphorus-doped diamond. In addition, it is correlated to their corrosion
resistance and mechanical stability.
The excellent corrosion resistance of nanocarbon ohmic contacts is then utilized to improve the
process flow of p-type diamond Schottky barrier diode fabrication procedure by avoiding the
post-annealing step that usually accompanies interface carbide forming ohmic contacts. The
diode parameters obtained through the proposed fabrication procedure exhibited good
uniformity with a very small standard deviation. Herein, this study suggests the possible
application of nanocarbon ohmic contacts over conventional Ti-based ohmic contacts for
diamond electronics. This thesis comprises six chapters elaborating the research findings as
follows

Chapter 1: This chapter provides the material characteristics of the diamond as a wide bandgap
semiconductor including its structural, mechanical, optical, and electronic properties. Through
mentioning the essential material properties, current methods of diamond fabrication are
discussed subsequently. Then, the recent advances in diamond doping and their applications in
realizing state of art practical devices are comprehended. As this study focuses on efficient
nanocarbon ohmic electrodes for semiconducting diamonds, recent ohmic contact strategies
reported for both phosphorus and boron-doped diamonds are emphasized in detail in this chapter.
Chapter 2: The chapter focuses on the fabrication of nanocarbon films on diamond substrates
and their structural characterization. Moreover, their structural properties are compared with
nanocarbon films fabricated on silicon substrates. The chapter provides a detailed explanation
of the basic nanocarbon fabrication method used for the complete study, that is coaxial arc
plasma deposition (CAPD). Furthermore, the calibration of the oxygen plasma condition is
demonstrated for the first time through visible Raman spectroscopy and scanning electron
microscopy (SEM) for the enhancement of spectral response from composite nanodiamond
grains in the nanocarbon film fabricated by CAPD.
Chapter 3: In this chapter, nanocarbon ohmic electrodes with enhanced carrier collection
efficiency were deposited by coaxial arc plasma deposition. The fabricated nanocarbon ohmic
electrodes were extensively studied in terms of specific contact resistance and corrosion
resistance. Circular transmission line model (cTLM) theory was used to estimate the charge
collection efficiency of the nanocarbon ohmic electrodes in terms of specific contact resistance
at a specific voltage range (5-10 V), they exhibited a specific contact resistance of 1×10-3 Ωcm2.
The result revealed one order reduction in the specific contact resistance and hence potential
drop at the diamond/electrode interface compared to the conventional Ti electrode.
Chapter 4: This chapter analyzes the contact behavior of n-type diamond/nanocarbon against
an extremely corrosive environment realized by boiling acid solution and they exhibited
excellent corrosion resistance and mechanical adhesion over conventional Ti-based contacts.
Even though more characterization focus is given to nanocarbon ohmic contacts on a
phosphorus-doped diamond, a similar trend is observed for nanocarbon contacts on boron-doped
diamonds also. The performance of nanocarbon ohmic contacts is strongly correlated with the
fabrication temperature, and the effect is discussed. The modest effect on the transfer length of
the nanocarbon contacts with respect to acid treatment sessions indicates a tightly bonded
diamond/nanocarbon interface and actively suggests their application in highly corrosive
environments.
Chapter 5: In this chapter, the effect on the uniformity of Schottky barrier diodes fabricated on
a wet chemically oxygen-terminated p-type diamond surface by avoiding the post-annealing step
through corrosion-resistant nanocarbon ohmic contacts is discussed. Due to the strong interface
because of partial sp3 interfacial bonds, the nanocarbon ohmic contacts are found withstandable
to wet chemical O-termination, unlike Ti contacts. The SBDs show good uniformity in their
ideality factor (mean value = 1.25) and Schottky barrier height (mean value = 1.45) with a
standard deviation of 0.04 and 0.03 respectively for 42 Schottky barrier diodes.
Chapter 6: Thesis summary and future perspectives of the Ph.D. research.