Noise Properties of GaN Nanowires

1
Noise Properties of GaN Nanowires

• L.C. Lia (???), Y. W. Suena(???) , T. C.
  Yeha(???),
• W. W. Chena(???), M. W. Leea(???) and C. C.
  Chenb(???)
• aDepartment of Physics, National Chung Hsing
  University, Taichung, Taiwan, R.O.C
• bDepartment of Chemistry, National Taiwan Normal
  University, Taipei, Taiwan, R.O.C

2
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.

3
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.12
• 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.345
• 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.

4
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 a1,
  b0, g is dimensionless.
• where NC is the
  number of charge carries.
• g2?10-3 in metal
  and semiconductor.1
• In the carbon nanotube experiment, the formula is
  applied
• where A is called
  noise magnitude.3
• A10-11R
• b11.1 for Single
  Wall Nanotube (SWNT) .
• For an individual Multiwalled Carbon Nanotube
  (MWNT), b1.02.
• For tow crossing Multiwalled Carbon
  Nanotube (MWNT), b1.56 .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.

5
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 preamplifier7
• Noise
  (with very high input
  impedance)
  
• If the cross spectrum technique
  is used, the noise will be down to
• 2.SR560 Low-noise preamplifier
  
• Noise
• 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.
  

6
Experimental Setup I Cross Spectrum
Measurement

• 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.

7
Experimental Setup II FFT Measurement

• 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.

8
Experimental Setup --The
Calculation

• From the small signal equivalent circuit (Fig.3)
  of our measurement setup, we can obtain
• Where R(R1R2)//R3//(R4R5)R6R7
• This illustrates that we should carefully check
  which one is the dominant noise, when we choose
  the resistor parallel to the sample.

Fig.3
9
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-Liquid-Solid (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. 89
• 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. Lees laboratory.
• The fig.4 is the SEM image of the sample 7-1-1.

10
Sample -- The electric property
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.

11
System Background Noise

• 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.

12
Results -- The noise of the metal film
resistors

• 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.

13
Results -- The spectrum of the sample

• 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.

14
Results -- The Hooge parameter of the Samples

• The Hooge parameter is obtained from the data
  between 0.5Hz and 8Hz..
• For R34.205kW (sample 7-1-1), the average Hooge
  parameter is 1.007 0.045 in Igt30nA. For
  R872.866kW (sample 7-2-1), the average Hooge
  parameter of the sample7-2-1 is 1.097 0.084 in
  Igt0.835nA.

15
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, 0.1nA100nA. In the bandwidth
  from 0.5Hz to 8Hz at the room temperature, the
  Hooge parameter is very close to one.

16
References

• P. Dutta and P. M. Horn, Rev. Mod. Phys. 53, 497
  (1981).
• 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).
• 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).
• ???, ????????????????, ???????????????? (2001)
• 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)
• 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.