Atmospheric Pressure Microplasma Treatment of GaN Surface
Yuta NOMA, Marius BLAJAN, Sigeya NARITSUKA and Kazuo SHIMIZU
Organization for Innovation and Social Collaboration, Shizuoka University,Johoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

INTRODUCTION(2) Experimental setup

XPS analysis

In this article, we present the investigation resultof GaN surface modification by microplasma
under atmospheric pressure.
GaN is usually formed by nitriding GaAs andgrown on the sapphire substrate with a highdislocation density. The large lattice mismatchbetween GaN crystal and sapphire substrateleads to the possibility of high threading
dislocations densities in the nitride layers.
Dislocations which occur in the GaN crystal
degenerate its quality and electric characteristic.
Plasma process for interface treatment, nitriding
process of GaAs and regrowth of GaN crystal wasinvestigated as the convenient way to reduce
dislocations of GaN crystal.
The use and possibility of atmospheric pressure
microplasma for reducing dislocations or crystal
growth of GaN was confirmed by using X-ray
Photoelectron Spectroscopy (XPS) and Atomic
Force Microscope AFM) to check the chemical andphysical change of GaN surface after microplasma
treatment.

Fig. 3 shows the experimental setup for
surface treatment of GaN substrate. In thisstudy, a neon transformer was used as apower supply to generate microplasma.
Streamers were generated between electrodes
could generate various radicals and ions.
These active species could affect a target
surface [1].

Chemical bonds on the GaN substrate surface
were analyzed by XPS. Excited Ar species andmetastable N2 species were generated frommicroplasma, mainly contributed to surface
modification of GaN substrate. These activespecies have relatively long life time, thus
these active species could affect the GaNsurface.
Increases of N-Ga bonds which formed GaN
substrate was observed with Ar microplasma
treatment in a argon atmosphere. In contrast,
decreases of N-Ga bonds was observed with
N2 microplasma treatment in a nitrogen
atmosphere. It is confirmed that carrier gas
and atmosphere gas are important factors forsurface modification of GaN substrate.

METHODS(1) Microplasma Electrodes
Microplasma was generated with a pair ofelectrodes which covered with dielectric layer
and faced each other at small discharge gap
under 100 μm with a spacer. Due to smalldischarge gaps (0 ∼ 100μm) and to the assumed
specific dielectric constant of εr = 104, a highintensity electric field (107 ∼ 108 V/m) could beobtained with relatively low discharge voltage of
only about 1 kV. Therefore only a small size
reactor is necessary and the power consumption
is low.

Fig. 3 Experimental setup for surface treatment of
GaN substrate.
Table 1 Experimental conditions.

(a) AC-powered MP, 5 s.

(b) AC-powered MP, 30 s.

(c) Pulse-powered MP, 5 s.

(d) Pulse-powered MP, 30 s.

Atmosphere gas
ArN2Carrier gas
Carrier gas Flow rate [m/s]
Discharge voltage [kV]50.9

1.7Discharge gap [µm]100From GaN surface to electrode[mm]

1Fig. 5 N 1s peaks of GaN surface by XPS.

RESULT
AFM analysis

Structure of microplasma electrodesHole size： 1.6 mm
Total area of holes： 14 mm2Discharge gap： 100 μm
Distance between GaN surface and electrode： 1 mmA significant physical modification of GaN
surface was observed in both Ar and N2
microplasma treatment. In Ar microplasma
treatment, a high amount of radicals and excitedspecies derived from Ar attributed to physicalchange of GaN surface. This could be consideredthat the etching effect of Ar. In N2 microplasma
treatment, excited N2 or N radicals generated by
microplasma could have affected the dangling
bonds of GaN surface due to the chemical
reaction.

(a) AC-powered MP, 5 s.

(b) AC-powered MP, 30 s.

(c) Pulse-powered MP, 5 s.

(d) Pulse-powered MP, 30 s.

Fig. 6 Ga 3d peaks of GaN surface by XPS.

Fig. 1 Microplasma electrodes.

Figure 2 shows a current-voltage waveform
during generating microplasma. Spick current
occurred at rise and decay time of discharge
voltage. This is a typical waveform of dielectricbarrier discharge.

CONCLUSIONS
15 μm

In this study, the following conclusions wereobtained.
1.The
possibilityoftheGaN
surfacemodification by atmospheric microplasma hadconfirmed.

(a) AC-powered microplasma treatment.

(a) AC-powered microplasma.
15 μm

2.Increases of the N-Ga bonds was observed
by Ar microplasma treatment and decreasesof the N-Ga bonds was observed by N2microplasma.
3.Physical change of GaN surface wasobserved in both Ar and N2 microplasma
treatment. In Ar microplasma treatment, it
could be considered that the etching effect ofexcited Ar species. In N2 microplasma
treatment, excited N or N2 radicals affected toGaN surface due to the chemical reaction.

REFERENCE(b) Pulse-powered microplasma.
Fig. 2 Image of microplasma generation.

(b) Pulse-powered microplasma treatment.
Fig. 4 AFM images of GaN surface.

[1] K. Shimizu, A. Umeda, S. Muramatsu, M. Blajan, J.
Appl. Phys. 50, 08KA03-1 (2011).
[2] K. Shimizu, Y. Noma, M. Blajan and S. Naritsuka,
J. Appl. Phys. 51, 08HB05-1 (2012).