Increases of N-Ga bonds which formed GaN was observed at N 1s peaks and Ga 3d peaks after Ar microplasma treatment in a argon atmosphere.
Decreases of N-Ga bonds was observed at N 1s peaks and increase of N-Ga bonds was observed at Ga 3d peaks after N2 microplasma treatment in a nitrogen atmosphere. This could be considered that nitrogen on the GaN surface was come away from GaN surface by N2 microplasma surface treatment [6].

Basic study on modification of GaN surface
by atmospheric microplasma
Yuta NOMA, Marius BLAJAN and Kazuo SHIMIZU
Innovation and Joint Research Center, Shizuoka University,Johoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

INTRODUCTIONGaN is usually formed by nitriding GaAs and grownon the sapphire substrate with a high dislocation
density as shown in Fig. 1 [1]. For this dislocation,
microchannel epitaxy (MCE) or regrowth of GaN isrequired to reduce dislocations. Recently, plasma
treatment is used for interface treatment, regrowthof GaN and nitridation process of GaAs.
Microplasma is a atmospheric pressure nonthermal
plasma and a type of dielectric barrier discharge
which has small discharge gap under 100 μm which
requires relatively low discharge voltage of only
about 1 kV. The effect of surface treatment of GaN
by atmospheric microplasma was experimentallyinvestigated.

(2) Experimental setup(2) XPS analysis

Fig. 5 shows the experimental setup for surface
treatment of GaN substrate. In this study, anegative pulse power supply was used to generate
microplasma. Streamers were generated between
electrodes could generate various radicals and ions.
These active species could affect a target surface[2].
An X-ray Photoelectron Spectroscopy (XPS)
analysis and image of GaN surface by Field Emission
Scanning Electron Microscope (FE-SEM) wasperformed before and after microplasma treatment.

Chemical bonds on the GaN substrate surface wereanalyzed by XPS. Excited Ar species and metastableN2 species were generated from microplasma,
mainly contributed to surface modification of GaN
substrate. These active species have relatively longlife time, thus these active species could affect theGaN surface.
Increase of the N-Ga bonds could occur due to theAr microplasma which has a high potential. Thishigh potential affected the GaN surface or aproblem of changing surface potential on a GaN
surface (Fig. 7). In contrast, decreases of thepeaks was observed in N2 microplasma treatment.
A decrease of nitrogen on the GaN surface meansthat GaN surface became a nitrogen deficiency
state (Fig. 8). In this state there are somepossibilities of applying the nitriding process or
regrowth of GaN.

Fig. 5 Experimental setup for surface treatment ofGaN substrate.

Fig. 1 Image of dislocations of the GaN substrate.

METHODS(a) N 1s peaks by XPS.
Table 1 Experimental conditions.

Atmosphere gas(1) Microplasma Electrodes
Microplasma was generated with a pair of electrodes
which covered with dielectric layer and faced eachother at small discharge gap under 100 μm with aspacer. Due to small discharge gaps (0∼100μm) andto the assumed specific dielectric constant of εr =104, a high intensity electric field (107 ∼ 108 V/m)
could be obtained with relatively low dischargevoltage of only about 1 kV.

ArN2Carrier gas
Carrier gas Flow rate [m/s]

5Discharge voltage [kV]-1.3-1.6Discharge gap [µm]1000From GaN surface to electrode[mm]

1Treatment time [s]5 ～ 30(b) Ga 3d peaks by XPS.
Fig. 7 Ar microplasma treatment.

RESULT

Fig. 2 Microplasma electrodes.

Structure of microplasma electrodesHole size： 1.6 mm
Total area of holes： 14 mm2Discharge gap： 100 μm
Distance between GaN surface and electrode： 1 mm

(1) SEM image of GaN surface
Images of GaN surface was taken by FE-SEM tocheck a damage of GaN surface by microplasma
treatment and confirm a effect of reducing
dislocations of a GaN surface on a substrate(Fig. 6). All of following GaN sample surface
were treated for 10 s with Ar microplasma andN2 microplasma.

(a) N 1s peaks by XPS.

(b) Ga 3d peaks by XPS.
Fig. 8 N2 microplasma treatment.

Before treatment

CONCLUSIONSIn this study, the following conclusions wereobtained.

Fig. 3 Image of microplasma.
Fig. 3 shows the discharge voltage and dischargecurrent waveform during generating microplasma.
Pulse width was about 1 μs and frequency was 1kHz.

Ar pulsed microplasma

N2 pulsed microplasma

1. The possibility of the GaN surface modification
by atmospheric microplasma had confirmed.
2. It could be considered that physical damage for
GaN surface can control by choosing
appropriate process gas, power supply andtreatment time.
3. Different changings of N 1s and Ga 3d peaks
was observed in Ar microplasma treatment andN2 microplasma treatment.

REFERENCEFig. 4 Discharge voltage and current waveform.

Ar AC microplasma
N2 AC microplasma
Fig. 6 Images of GaN surface.

[1] X. H. Wu, L. M. Brown, D. Kapolnek, S. Keller, B. Keller, S. P.
DenBaars and J. S. Speck, J. Appl. Phys. 80, 3228 (1996).
[2] K. Shimizu, A. Umeda, S. Muramatsu, M. Blajan, J. Appl.
Phys. 50, 08KA03-1 (2011).