24P019-0
Basic Study on Surface Modification of GaN Substrateby Atmospheric Microplasma
大気圧マイクロプラズマによるGaN基板表面改質の基礎検討
1Yuta Noma, Marius Blajam, Shigeya Naritsuka and Kazuo Shimizu
野間 悠太, 1マリウス ブラジャン，2成塚 重弥，1清水 一男
1Shizuoka University, Innovation and Joint Research Center
3-5-1, Johoku, nakaku, Hamamatsu 432-8561, Japan
静岡大学イノベーション共同研究センター 〒432-8561 浜松市中区城北3-5-1
2Meijo University, Department of Materials Science and Engineering

1-501, Shiogamaguti, Tenpakuku, Nagoya 468-8502, Japan
名城大学理工学部材料機能工学科 〒468-8502 名古屋市天白区塩釜口1-501
GaN is widely studied and developing its growth material for new application such as powerdevice or emitting various color of light by adjusting its band gap by mixing it with Indium orAluminium. GaN is usually formed by nitriding GaAs and grown on the sapphire substrate with a highdislocation density. For this dislocation, microchannel epitaxy (MCE) or regrowth of GaN is required toreduce dislocations. Recently, plasma treatment is used for interface treatment, regrowing of GaN crystaland nitridation process of GaAs. In this article we present the investigation result of GaN surface
modification by microplasma under atmospheric pressure.

1. Introduction
GaN is well known material for blue LED andsemiconductor lasers. GaN is usually formed bynitriding GaAs and grown on the sapphire
substrate with a high dislocation density [1]. For
this dislocation, microchannel epitaxy (MCE) or
regrowth of GaN is required to reduce
dislocations [2]. Recently, plasma treatment isexpected for interface treatment, regrowth of GaN
and nitridation process of GaAs [3].
Effect on surface treatment of GaN substrateby microplasma under atmospheric pressure wascarried out [4].
2. Experimental Method
Figure 1 shows the schematic image of
microplasma electrodes for GaN surface treatment.
Microplasma was generated with a pair ofelectrodes covered with dielectric layer and faced
each other at a small discharge gap under 100 µm.
Due to a small discharge gaps and to the assumed
specific dielectric constant of εr = 104, a highintensity electric field (107 ∼ 108 V/m) could be

Fig. 1. Schematic image of microplasma electrodes.

obtained with relatively low discharge voltages
only about 1 kV. Streamers were generated between
electrodes could generate various radicals and ions.
These active species could affect a target surface.
Figure 2 shows the experimental setup for
surface treatment of GaN substrate. In theexperimental setup (a), surface treatment of GaN
substrate was performed in atmosphere with Ar
carrier gas. A marx generater, a negative pulse
power supply, was used for microplasma generation.
Discharge voltage of -1.3 kV, rise time of 50 ns,
pulse width of 3 µs and frequency of 24 kHz,energized the electrodes. Flow rate of Ar carrier gas
was set at 5 L/min. In the setup (b), experiment wasperformed in a nitrogen atmosphere with N2 carriergas. A neon transformer, a AC high voltage, wasused as a power supply. Discharge voltage of 1.5
kV and frequency of 27 kHz was energized theelectrodes. Flow rate of N2 carrier gas was set at 5L/min.
Contact angle on the GaN surface and an analysis
by X-ray Photoelectron Spectroscopy (XPS) wasmeasured before and after microplasma surface
treatment of GaN substrate.

(a) Ar plasma treatment in atmosphere.

(b) N2 plasma treatment in a nitrogen atmosphere.
Fig. 2. Experimental setups.

3. Experimental Result
3.1. Contact angle measurement
The contact angle of GaN surface was evaluatedby contact angle meter with a drop of distilled wateron the GaN surface. The contact angle wascalculated by the θ/2 method. Figure 3 shows
images of contact angle of GaN surface.

(a) Treated for10 s with Ar plasma.

(b) Treated for 30 s with N2 plasma.
Fig. 3. Image of contact angle measurement.
Initial contact angle of GaN surface was 65.8°. Adecrease of contact angle was observed aftermicroplasma treatment at both of experimental
conditions. The contact angle decreased at 22.6°
after Ar microplasma treatment applied for 10 s andat 26.1° after N2 microplasma treatment applied for
30 s. It could be considered that increase of thehydrophilic groups concerning with nitrogen.
3.2. XPS analysis
Chemical bonds on the GaN surface wereanalyzed by XPS. Figure 4 shows N 1s peaks of theGaN substrate surface.
On the Ar microplasma treatment in atmosphere,a increase of the N-Ga bond which formed GaN
was observed. It could be considered that Ar plasma
which has a high potential about 11.5 eV affected
to GaN substrate surface.
In contrast, a decrease of the N-Ga bond wasobserved with experimental condition of N2
microplasma treatment in a nitrogen atmosphere.
This could be considered that the nitrogen atoms on
the GaN substrate surface were decreased by N2plasma treatment.

(a) N 1s peaks treated with Ar microplasma.

(b) N 1s peaks treated with N2 microplasma.
Fig. 4. N 1s peaks by XPS.
4. Conclusions
In this study, the following conclusions wereobtained.
1. The possibility of the GaN surface
modification by atmospheric microplasma hadconfirmed.
2. A decrease of a contact angle was observed atboth of experimental conditions. It could beconsidered that increase of the hydrophilicgroups concerning with nitrogen at both ofexperimental conditions.
3. A increase of the N-Ga bond was observed by
Ar microplasma treatment in atmosphere. It
could be considered that Ar plasma which has
high potential affected to GaN substratesurface.
A decrease of the N-Ga bond was observed byN2 microplasma treatment in a nitrogenatmosphere. It could be considered that thenitrogen atoms on the GaN substrate surface
were decreased by N2 plasma treatment.
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