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Noise Properties of GaN Nanowires
L.C. Lia (李良箴), Y. W. Suena(孫允武) , T. C. Yeha(葉宗祺),
W. W. Chena(陳文威), M. W. Leea(李明威) and C. C. Chenb(陳家俊)
aDepartment
of Physics, National Chung Hsing University, Taichung, Taiwan, R.O.C
bDepartment
of Chemistry, National Taiwan Normal University, Taipei, Taiwan, R.O.C
Abstract
We will report the noise behavior of GaN nanowires
at the room temperature. The typical resistances of
the samples are from few kW to hundreds of kW at
room temperature. The resistance increases to few
MW at 77K. We use cross spectrum and FFT
technique to measure the noise properties of these
nanowires. The GaN nanowires exhibit the 1/f noise
in the current range, 0.1nA ~70nA. The Hooge
parameter of the 1/f noise of these wires is around 1.
Introduction
 The fluctuation of the condense matter links to the physical
phenomena. The 1/f noise arises due to the relaxation of the
defects or the dynamics of groups of defects in a finite relaxation
time. That means the study of 1/f noise is an issue to understand
the physical properties of the condense matter.[1][2]
 For the conventional electronic material, the magnitude of the
1/f noise would take into consideration in assessing the potential
for electronic and sensor application.
 In recent years, the carbon nanotube is a well-studied
mesoscopic device. There is the large magnitude of the noise
observed.[3][4][5]
 It is important to study the 1/f noise of the GaN nanowires.
Apart from evaluating the potential of this nanowire as a device,
the physical phenomena are worthy to understand.
The 1/f Noise
--The Brief Review
 It is indicated that the 1/f noise is the noise which is relative to the
frequency.[6]
only when a=1, b=0, g is dimensionless.
V 2 b
where NC is the number of charge carries.
SV  g
a
NC f
g=210-3 in metal and semiconductor.[1]
 In the carbon nanotube experiment, the formula is applied:
where A is called noise magnitude.[3]
2
V
A=10-11R
SV  A b
f
b=1~1.1 for Single Wall Nanotube (SWNT) .
 For an individual Multiwalled Carbon Nanotube (MWNT), b=1.02.
For tow crossing Multiwalled Carbon Nanotube (MWNT), b=1.56 .[5]
 In our experiment, we measured the 1/f noise for the frequency
below 50Hz. Our results show that the GaN nanowires also exhibit
the 1/f-like excess noise. We also note that the 1/f noise of the
nanowires exists in a lower frequency range than that of the carbon
nanotubes.
Experimental Setup
 In this experiment, we use a balanced circuit to measure the noise of an GaN
nanowire. There are two methods in our measurement. One is the cross
spectrum technique. The other is using the FFT technique directly. We use the
SR780 spectrum analyzer.
 The specification of our instruments:
1.Homemade JFET-input low-noise voltage preamplifier[7]:
Noise: 1.95nV/ Hz at 1kHz
(with very high input impedance)
If the cross spectrum technique is used, the noise will be down to 0.3nV/ Hz
2.SR560 Low-noise preamplifier:
Noise  4nV/ Hz at 1kHz
3.SR780 Spectrum Analyzer:
Full span: 102.4kHz
 The measurable bandwidth is decreased as the resistant of the sample is
increased. Even though the 1/f noise we study is below 50Hz, the bandwidth
still be carefully checked.
Experimental Setup I
– Cross Spectrum Measurement
+
-
SR780
Sample
+
Fig.1
 The Fig. 1 is shown the symmetry circuit. The amplifiers are including the
homemade JFET preamplifiers and the SR560 low noise preamplifiers. By
the use of the two synchronous sampling channels of the SR780 spectrum
analyzer, the cross spectrum can be obtained.
Experimental Setup II
– FFT Measurement
Sample
+
-
SR780
Fig.2
 In the direct FFT measurement, the amplified signal is directly fed into the
SR780. The data can be calculated by the spectrum analyzer in the power
spectrum density unit.
Experimental Setup
--The Calculation
 From the small signal equivalent
circuit (Fig.3) of our measurement
setup, we can obtain:
S m  Vns  2 (
  I ns  2 (
R
)2
R  Rsample
R  Rsample
R  Rsample
  VR  2 (
Rsample
RR
)2
)2
sample
 Where
R=[(R1+R2)//R3//(R4+R5)]+R6+R7
 This illustrates that we should
carefully check which one is the
dominant noise, when we choose the
resistor parallel to the sample.
Fig.3
Sample
 The nanowire samples are provided by Dr.C.
C. Chen of the Department of Chemistry in
the National Taiwan Normal University. The
nanowires are grown by the Vapor-LiquidSolid (VLS）method. By applying different
metal nanoparticles as the accelerant, the Ga
bulk is put into the quartz tube and heated to
910℃ in an increasing rate 50℃ /min. The flow
of NH3 is controlled at 18 sccm. The reaction
time is 12hours. [8][9]
 The electrodes of the nanowires are defined by
the e-beam lithography. The Ti/Au is chosen as
the ohmic contact for these wires. The device is
made by Dr. M.W. Lee’s laboratory.
 The fig.4 is the SEM image of the sample 7-1-1.
Fig.4
Sample
-- The electric property
-7
1.0x10
-8
8.0x10
I=2.92348E-5V+6.47417E10, R=34.205k
-7
1.5x10
I=1.14565E-6V-1.1877E-9, R=872.866kW
Sample 7-2-1
linear fit
Sample 7-1-1
linear fit
-7
1.0x10
-8
6.0x10
-8
-8
5.0x10
Current(A)
Current (A)
4.0x10
-8
2.0x10
0.0
-8
0.0
-2.0x10
-8
-5.0x10
-8
-4.0x10
-8
-6.0x10
-7
-1.0x10
-8
-8.0x10
-7
-7
-1.0x10
-0.003
-0.002
-0.001
0.000
Voltages (V)
0.001
0.002
0.003
-1.5x10
-0.10
-0.05
0.00
Voltages(V)
0.05
0.10
Fig.5
 Fig.5 is the I-V plots of two samples at the room temperature. The resistant
are 34kW and 872.866kW, respectively, by use of the slope from the linear
fitting.
System Background Noise
Span=50Hz
1E-16
Full Span
1E-16
1E-17
1E-17
SV (V /Hz)
SV (V /Hz)
1E-18
2
2
1E-18
1E-19
1E-19
1E-20
1E-20
1
10
Frequency (Hz)
1E-21
100
1000
10000
100000
Frequency (Hz)
Fig.6
 It is important to calibrate the system background noise. As the graphs shown,
the background noise is smaller than 1× 10-16 V2/Hz. For our samples, the
resistant is from 104 W to 106 W and the typical thermal noise is from 10-16
V2/Hz to 10-14 V2/Hz, respectively. Therefore, this system is good enough to
measure the noise.
Results
-- The noise of the metal film resistors
R=22kW
6E-16
R=506kW
1E-13
I=0.5nA
I=5nA
I=50nA
5.5E-16
5E-16
I=0.1403nA
I=1.0909nA
I=5.1225nA
I=10.1186nA
SV(Vrms/Hz)
4E-16
2
2
SV(Vrms/Hz)
4.5E-16
3.5E-16
1E-14
3E-16
2.5E-16
1E-15
2E-16
1
10
Frequency (Hz)
1
10
Frequency (Hz)
Fig.7
 The metal film resistors are taken as the standard samples in this experiment.
We take these resistors which resistant is about the same as the resistant of the
GaN nanowires. The pink line in the plot is the thermal noise of the resistors.
From the figure, the data indicates that the metal film resistor has very small
1/f noise when the external current is applied.
Results
-- The spectrum of the sample
Sample7-1-1 R=34.205kW
Sample7-2-1 R=872.866kW
1E-8
I=0.88nA
I=0.25nA
I=0.75nA
I=1.06nA
I=2.17nA
I=3.16nA
I=4.01nA
I=5.13nA
I=5.97nA
I=7.06nA
I=8.16nA
I=9.04nA
I=6.1nA
I=9.6nA
1E-9
I=12nA
I=19nA
1E-13
I=26nA
I=33nA
1E-10
I=39nA
I=45nA
SV(Vrms/Hz)
I=57nA
1E-11
I=65nA
1E-14
2
2
SV(Vrms/Hz)
I=52nA
1E-12
1E-13
1E-15
1E-14
1E-16
1E-15
1
10
Frequency (Hz)
1
10
Frequency (Hz)
 The nanowire is different from the metal film resistor. There is excess noise
raising up when the current through the GaN-nanowire is increased. The
orange straight line the plot is the basic thermal noise.
Results
-- The Hooge parameter of the Samples
1.4
Sample 7-1-1, R=34.205kW
Sample 7-2-1, R=872.866kW
1.2
1.0
0.8
a
 The Hooge parameter is obtained
from the data between 0.5Hz and
8Hz..
 For R=34.205kW (sample 7-1-1),
the average Hooge parameter is
1.007± 0.045 in I>30nA. For
R=872.866kW (sample 7-2-1), the
average Hooge parameter of the
sample7-2-1 is 1.097± 0.084 in
I>0.835nA.
0.6
0.4
0.2
1E-10
1E-9
1E-8
Current (A)
1E-7
Conclusion
Comparing the noise of the metal film resistor
with the noise of the GaN nanowires, the GaN
nanowires clearly exhibit the excess 1/f noise.
The smaller resistant of the GaN nanowire is,
the lower frequency the 1/f noise is exhibited in.
We measure the 1/f noise of the GaN nanowire
in the current range, 0.1nA~100nA. In the
bandwidth from 0.5Hz to 8Hz at the room
temperature, the Hooge parameter is very close
to one.
References
1.
P. Dutta and P. M. Horn, Rev. Mod. Phys. 53, 497 (1981).
2.
3.
A. K. Raychaudhuri, Curr. Opin. Solid State Mater. Sci. 6, 67 (2002).
P. G. Collins, M. S. Fuhrer, and A. Zettl, Appl. Phys. Lett. 76, 894
(2000).
4.
E. S. Snow, J. P. Novak, M. D. Lay, and F. K. Perkins, Appl. Phys. Lett.
85, 4172(2004). F. N.
H. Ouacha, M. Willander, H. Y. Yu, Y. W. Park, M. S. Kabir, S. H.
Magnus Persson, L. B. Kish, and A. Ouacha, Appl. Phys. Lett. 80, 1055
(2002).
Hooge, Phys. Lett. A 29, 139 (1969).
5.
6.
7.
王文凱, 低雜訊前級放大器製作與雜訊之量測, 國立中興大學物理系大
學部畢業論文 (2001)
8.
C.C.Chen, C.C.Yeh, C.H.Chen, M.Y.Yu, H.L.Liu, J.J.Wu, K.H.Chen,
J.Y.Peng, Y.F.Chen, J. Am. Chem. Soc. 123, 2791. (2001)
9.
S.Dhara, A.Datta, C.T.Wu, Z.H.Chen, Y.L.Wang, L.C.Chen,
C.W.Hsu,H.M.Lin, C.C.Chen, Appl. Phys. Lett. 82, 451.