Non-local Low-Frequency Non-equilibrium Excess Noise of GaN Nanowires
L. C. Li1, K. H. Huang1, Y. W. Suen1*, W. H. Hsieh2, C. D. Chen2, M. W. Lee1,
T. W. Liu3 and C. C. Chen3
1
Department of Physics, National Chung Hsing University, Taichung,, Taiwan, R.O.C.
2
Institute of Physics, Academia Sinica, Taipei, Taiwan, R.O.C.
3
Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan, R.O.C.
A non-local characteristic in the low-frequency non-equilibrium excess noise of a
GaN nanowire is found by checking the correlation of the electric fluctuations from
adjacent parts of the same nanowire. This correlated part of the excess noise can be
separated into a 1/f-noise spectrum and a Lorentzian-like spectrum.We investigated
several GaN nanowires of width from 80 to 150 nm grown by Vapor-Liquid-Solid
method.[1] Four 300-400 nm-wide Al electrodes connected to the nanowire are
defined by e-beam lithography. The resistances of the nanowire and the contacts can
be identified by examining the multi-wire resistance measurements, the thermal noise
spectrum, and also the cross spectrum between different sets of contacts; they are
ranging from few kilo ohms to hundreds of kilo ohms at room temperature. The
voltage noise power spectral density (PSD) is measured from 10mHz to 10kHz. While
applying various bias current (I) from 1 to 10nA through the nanowire , we can
observe that the PSD of the low-frequency excess noise, which is in the form of
1/f-noise, increases with I and follows Hooge's phenomenological equation
Sf=(A*V^2)/f ^b, where A is the noise magnitude, V is the voltage across the
nanowire, and b is a constant close to 1.[2]
In the thermal noise dominated region, the resistances of the nanowire and contacts
consist with the calculated results from the measured thermal noise. However, the
cross spectrum between different parts of the nanowires shows an anomalous
enhancement in the 1/f-like noise region with a non-zero bias current. This
observation strongly implied that the current fluctuations from different parts of the
nanowire are correlated; that is to say the low-noise fluctuations in a nanowire are
non-local. For large enough I, we also observe a Lorentzian-like spectrum embedded
in the 1/f-like spectrum. The characteristic time associated with the Lorentzian
spectrum is about 0.1s to 1s.
From our data of different samples and I’s, we obtain b=1.04±0.07 in average. A is
ranging from 8*10^-9 to 2*10^-6 (V is in the unit of volt and f in Hz), and keeps at
about the same value for each individual sample at different I.
The level of correlation of the fluctuations depends on the bias current I and f. We can
use a correlation coefficient (Cf) to quantify this effect; thus, the enhancement part of
the cross spectrum can be written as Cf*|Vn1|*|Vn2|. Cf is almost zero in the white
thermal noise region, and has a significant number in the low-frequency excess noise
region.
In conclusion, we have observed a non-local effect in the non-equilibrium excess
noise in GaN nanowires, and this excess noise consists of 1/f noise and
Lorentzian-like noise.
*Corresponding author: Y. W. Suen, email: ysuen@phys.nchu.edu.tw
[1] 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).
[2] Hooge, Phys. Lett. A, 29, 139 (1969); P. Dutta and P. M. Horn, Rev. Mod. Phys.,
53, 497 (1981).