1/f noise investigation was performed on n-GaN epitaxial layer grown on sapphire. The variation of spectral power density of voltage fluctuations density was observed as a function of frequency (100-50 Hz) and it showed the 1/f spectra. This type of
behavior was attributed to the presence of traps. The variation in spectral power density of voltage fluctuations with temperature was also observed with in the temperature range 80 K and 300 K and it was found to be slightly increasing with
temperature. It was attributed to the trapping-detrapping process of charge carriers by the defects. Four probe configuration was used for noise measurement and contacts
were made with indium. To check the stability and ohmic behavior of contacts, I-V measurements were performed with in the temperature range 80-325 K.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2201

Asokan, K.

Kumar, Ashish

Kumar, Ashutosh

Kumar, V.

Singh, R.

SocioEconomic Challenges Journal (Sumy State University)

 
 
 
J. Nano- Electron. Phys. 
3 (2011) No1, P. 676-679 
Ó 2011 SumDU 
(Sumy State University) 
 
 
676 
PACS numbers: 73.50.Td, 73.61.Ey, 72.20.Jv, 73.40.Cg 
 
TEMPERATURE DEPENDENCE OF 1/f NOISE IN GALLIUM NITRIDE 
EPITAXIAL LAYER  
 
Ashutosh Kumar1, Ashish Kumar1, K. Asokan2, V. Kumar1, R. Singh1 
 
1 Indian Institute of Technology, Delhi 
 Hauz Khas, 110016, New Delhi, India 
 E-mail: vkmr@physics.iitd.ac.in 
2 Inter University Accelerator Centre, 
 Arun Asif Ali Marg, 110067, New Delhi, India 
 E-mail: kasokan@iuac.ac.in 
 
1/f noise investigation was performed on n-GaN epitaxial layer grown on sapphire. 
The variation of spectral power density of voltage fluctuations density was observed 
as a function of frequency (100-50 Hz) and it  showed the 1/f  spectra.  This  type of  
behavior was attributed to the presence of traps. The variation in spectral power 
density of voltage fluctuations with temperature was also observed with in the 
temperature range 80 K and 300 K and it was found to be slightly increasing with 
temperature. It was attributed to the trapping-detrapping process of charge carriers by 
the defects. Four probe configuration was used for noise measurement and contacts 
were made with indium. To check the stability and ohmic behavior of contacts, I-V 
measurements were performed with in the temperature range 80-325 K. 
 
Keywords: 1/f NOISE, SPECTRAL POWER DENSITY, VOLTAGE FLUCTUATIONS, 
OHMIC CONTACTS, TRAPS, TEMPERATURE. 
 
(Received 04 February 2011) 
 
1. INTRODUCTION 
 
The study of the 1/f noise  is  important  both  from  fundamental  as  well  as  
technological point of view, since it sets the limit to the ultimate resolution 
achieved with the devices made from the materials [1-3]. If a constant voltage 
is applied to a semiconductor sample or device, to a resistor or vacuum tube, 
the current will exhibit fluctuations. The frequency spectrum is in general 
constant at high frequencies, superimposing with shot-noise components. 
However, at low frequency f, (f < 100 Hz), spectral power density of voltage 
fluctuations  is found to be proportional to 1/f g (g in the range 0.8-1.2) [6]. 
This kind of noise is frequently called as low-frequency noise, flicker noise or 
1/f noise. The 1/f noise observed in semiconductors arises due to presence of 
traps having wide distribution of activation energies [2]. Although the low-
frequency fluctuation phenomenon are also observed in other non-electronic 
systems,  such  as  earth  rotation  frequency,  loudness  of  speech,  nerve  
membrane potential, highway traffic current etc, none of them is as crucial as 
the noise in electronic systems because the noise directly deteriorates the 
device and system performances [2]. We report here 1/f conduction noise 
studies performed on MOCVD grown n-GaN epitaxial layer on sapphire. 
Ohmic contacts were made with indium and in order to check the stability of 
contacts,  I-V  measurements  were  performed  from  80  K  to  325  K.  The  
variation of spectral noise density with temperature was also investigated. 
 
 
 
 TEMPERATURE DEPENDENCE OF 1/f NOISE IN… 677 
2. EXPERIMENTAL WORK 
 
To measure 1/f noise and I-V, we had employed standard four probe detection 
method. The sample used in present study was cut from 2 inch epitaxial layer 
grown  on  sapphire.  The  dimension  of  sample  was  1cm  by  1cm  by  3  µm.  
Sample  was ultrasonically  cleaned using TCE, acetone,  DI water  and finally  
dipped  for  2  min  in  Hydrochloric  acid.  Contacts  were  made  manually  with  
indium and in order to ensure the ohmic behaviour and thermal stability of 
contacts, I-V measurements were done from 80 K to 325 K. For I-V and noise 
measurement, the sample was mounted in the cryostat and a rotary pump was 
used  to  have  a  vacuum  of  the  order  of  2.5×10- 2 mbar. The electrical 
connections  from  the  sample  were  taken  out  (from  cryostat  to  measuring  
circuitry) using the vacuum compatible BNC cables and connectors.  
 For  I-V  measurements,  Keithley  2612  A  source  meter  was  used  and  
voltage (- 5  V to  + 5 V)  was applied across  the sample.  A heater  of  50 W, 
40 V was used for heating from liquid nitrogen temperature to 325 K. 
Lakeshore  340  temperature  controller  was  used  for  controlling  the  
temperature and Pt-100 sensor was used for detecting temperature. 
 1/f noise  was measured using the four probe method.  The setup for  the 
noise is shown below. A dc current was passed through the two probes of the 
sample using battery operated dc current source (consisting of a 9 V battery 
and a variable resistance). The voltage developed across the sample was fed to 
a  low  noise  preamplifier  (model  SR  552,  Stanford,  USA).  The  preamplifier  
blocks the dc component of voltage and allows only the ac component to pass 
through it. The amplified ac signal was then fed to a HP spectrum analyser 
that  displayed  the  spectral  power  density  of  voltage  fluctuation  (Sv) as a 
function of frequency (f). For determining 1/f noise with frequency, we took 
the noise spectra with and without (consisting of preamplifier + thermal noise) 
current.  Then  the  latter  spectrum  was  subtracted  from  the  former,  and  we  
obtained pure 1/f noise spectrum that was due to the conductivity fluctua-
tions inside the sample. The background noise spectrum showed a 1/f contribu-
tion arising from the preamplifier for frequencies < 5 Hz. Above 5 Hz, back-
ground noise remains constant (frequency independent white noise). We could 
achieve a sensitivity of 2.5×10- 18 V 2/Hz at room temperature and 10 Hz. 
 
 
 
Fig. 1 - 1/f noise measurement setup 
 
 In order to study the temperature variation, the sample was loaded in the 
cryostat. The temperature was varied between 80 K and 300 K using 
Lakeshore  340  temperature  controller.  Pt  -  100  sensor  was  used  for  
detecting the temperature and cartridge heater was used for the heating 
purpose. Before taking the noise reading at any value, the temperature was 
stabilized within 10 mK. 
 
 
 
678 ASHUTOSH KUMAR, ASHISH KUMAR, K. ASOKAN, ET AL.  
3. RESULTS AND DISCUSSION 
 
Contacts  play  an  important  role  in  1/f noise studies [5, 7] so it is very 
important to check the stability of contacts with in the temperature range in 
which 1/f noise investigation has to be done. So in order to check the stability 
of contacts, I-V measurements were done at various temperatures in the 
temperature range 80 K - 325 K. The straight line at each temperature 
ensures  that  contacts  were  ohmic.  I-V  at  different  temperatures  for  n-GaN  
epitaxial layer grown on sapphire with indium contacts is shown in Fig. 2. 
 
 
 
Fig. 2 - V-I at different temperatures 
 
 The variation in spectral power density of voltage fluctuations (Sy) with 
frequency (f) was observed at various temperatures in the frequency range 
100  mHz  to  50  Hz.  The  variation  in  spectral  power  density  of  voltage  
fluctuation with frequency at 80 K and 300 K is shown in Fig. 3. 
Theoretical 1/f line was also plotted. The deviation of the experimental 
results from the theoretical 1/f line  can be explained by Hooge Model  [1],  
which states that spectral power density of voltage fluctuations (Sv) varies 
as 1/f γ and g varies between 0.8-1.2. 
 
 
 
Fig. 3 - Spectral voltage noise density as a function of frequency at 80 K and 300 K 
 
1/f noise is more at lower frequency side and it is due to presence of large 
number of traps having wide distribution of relaxation time and it is found that 
in semiconductors spectral power density becomes frequency dependent [3]. If t 
is the relaxation time for a trap, then spectral power density is given as 
 
 S (f) ~ 2t / (1 + (2pft) 2) (1) 
 
 
 
 
 TEMPERATURE DEPENDENCE OF 1/f NOISE IN… 679 
 At the lower frequency (f << 1/t,) S (f) = constant and at high frequency 
(f >> 1/t), S (f) ~ 1/f². In the presence of distribution of relaxation time, by 
averaging the spectrum at different relaxation time, we get 1/f spectrum [2]. 
 At f = 10 Hz, the variation of spectral power density of voltage 
fluctuations (Sv) with temperature was observed and it is shown in Fig. 4. 
Sv was found to be slightly increasing with in temperature range 80-300 K. 
As temperature increases, more defects will become mobile and participate 
in the trapping-detrapping of charge carriers [4]. So fluctuation in the 
conductivity is more due to this trapping and detrapping process, spectral 
power density of voltage fluctuations increases.  
 
 
 
 Fig. 4 - Spectral voltage noise density as a function of temperature at f = 10 Hz 
 
4. CONCLUSION 
 
We have observed the 1/f variation of spectral noise voltage density with 
frequency at the lower frequency side (100-50 Hz). The origin of this type of 
noise in semiconductors is attributed to the presence of traps. The 
temperature variation of the noise is also investigated ant it is attributed to 
the  trapping-detrapping  process.  Contacts  plays  an  important  role  in  1/f 
noise studies so I-V was done at each temperature of the noise measurement 
and at each temperature, contacts were found to be ohmic. 
 
Ashutosh  Kumar  is  grateful  to  the  Dr.  D.  Kanjilal  of  Inter  University  
Accelerator  Centre,  New Delhi  for  his  support  during this  work.  Ashutosh 
Kumar is also thankful to CSIR for research fellowship. 
 
REFERENCES 
1. F.N. Hooge, IEEE T. Electron. Dev. 41, 1926 (1994). 
2. A.K. Raychaudhari, Curr. Opin. Solid St. M. 67, 6 (2002). 
3. L.K.J. Vandamme, X. Li, D. Rigaud, IEEE T. Electron Dev. 41, 1936 (1994). 
4. H. Wong, Microelectron. Reliab. 43, 585 (2003). 
5. B.H. Leung, W.K. Fong, C. Surya, Opt. Mat. 23, 203 (2003). 
6. R. Singh, D. Kanjilal, J. Appl. Phys. 91, 411 (2002). 
7. N. Tanuma, M. Tacano, J. Pavelka, S. Hashiguchi, J. Sikula, T. Matsui, Solid-
State Electron. 49 865 (2005). 


English

Temperature dependence of 1/f noise in Gallium Nitride epitaxial layer

Electronic Sumy State University Institutional Repository

   J. Nano- Electron. Phys. 3 (2011) No1, P. 676-679 Ó 2011 SumDU (Sumy State University)   676 PACS numbers: 73.50.Td, 73.61.Ey, 72.20.Jv, 73.40.Cg  TEMPERATURE DEPENDENCE OF 1/f NOISE IN GALLIUM NITRIDE EPITAXIAL LAYER   Ashutosh Kumar1, Ashish Kumar1, K. Asokan2, V. Kumar1, R. Singh1  1 Indian Institute of Technology, Delhi  Hauz Khas, 110016, New Delhi, India  E-mail: vkmr@physics.iitd.ac.in 2 Inter University Accelerator Centre,  Arun Asif Ali Marg, 110067, New Delhi, India  E-mail: kasokan@iuac.ac.in  1/f noise investigation was performed on n-GaN epitaxial layer grown on sapphire. The variation of spectral power density of voltage fluctuations density was observed as a function of frequency (100-50 Hz) and it  showed the 1/f  spectra.  This  type of  behavior was attributed to the presence of traps. The variation in spectral power density of voltage fluctuations with temperature was also observed with in the temperature range 80 K and 300 K and it was found to be slightly increasing with temperature. It was attributed to the trapping-detrapping process of charge carriers by the defects. Four probe configuration was used for noise measurement and contacts were made with indium. To check the stability and ohmic behavior of contacts, I-V measurements were performed with in the temperature range 80-325 K.  Keywords: 1/f NOISE, SPECTRAL POWER DENSITY, VOLTAGE FLUCTUATIONS, OHMIC CONTACTS, TRAPS, TEMPERATURE.  (Received 04 February 2011)  1. INTRODUCTION  The study of the 1/f noise  is  important  both  from  fundamental  as  well  as  technological point of view, since it sets the limit to the ultimate resolution achieved with the devices made from the materials [1-3]. If a constant voltage is applied to a semiconductor sample or device, to a resistor or vacuum tube, the current will exhibit fluctuations. The frequency spectrum is in general constant at high frequencies, superimposing with shot-noise components. However, at low frequency f, (f < 100 Hz), spectral power density of voltage fluctuations  is found to be proportional to 1/f g (g in the range 0.8-1.2) [6]. This kind of noise is frequently called as low-frequency noise, flicker noise or 1/f noise. The 1/f noise observed in semiconductors arises due to presence of traps having wide distribution of activation energies [2]. Although the low-frequency fluctuation phenomenon are also observed in other non-electronic systems,  such  as  earth  rotation  frequency,  loudness  of  speech,  nerve  membrane potential, highway traffic current etc, none of them is as crucial as the noise in electronic systems because the noise directly deteriorates the device and system performances [2]. We report here 1/f conduction noise studies performed on MOCVD grown n-GaN epitaxial layer on sapphire. Ohmic contacts were made with indium and in order to check the stability of contacts,  I-V  measurements  were  performed  from  80  K  to  325  K.  The  variation of spectral noise density with temperature was also investigated.     TEMPERATURE DEPENDENCE OF 1/f NOISE IN… 677 2. EXPERIMENTAL WORK  To measure 1/f noise and I-V, we had employed standard four probe detection method. The sample used in present study was cut from 2 inch epitaxial layer grown  on  sapphire.  The  dimension  of  sample  was  1cm  by  1cm  by  3  µm.  Sample  was ultrasonically  cleaned using TCE, acetone,  DI water  and finally  dipped  for  2  min  in  Hydrochloric  acid.  Contacts  were  made  manually  with  indium and in order to ensure the ohmic behaviour and thermal stability of contacts, I-V measurements were done from 80 K to 325 K. For I-V and noise measurement, the sample was mounted in the cryostat and a rotary pump was used  to  have  a  vacuum  of  the  order  of  2.5×10- 2 mbar. The electrical connections  from  the  sample  were  taken  out  (from  cryostat  to  measuring  circuitry) using the vacuum compatible BNC cables and connectors.   For  I-V  measurements,  Keithley  2612  A  source  meter  was  used  and  voltage (- 5  V to  + 5 V)  was applied across  the sample.  A heater  of  50 W, 40 V was used for heating from liquid nitrogen temperature to 325 K. Lakeshore  340  temperature  controller  was  used  for  controlling  the  temperature and Pt-100 sensor was used for detecting temperature.  1/f noise  was measured using the four probe method.  The setup for  the noise is shown below. A dc current was passed through the two probes of the sample using battery operated dc current source (consisting of a 9 V battery and a variable resistance). The voltage developed across the sample was fed to a  low  noise  preamplifier  (model  SR  552,  Stanford,  USA).  The  preamplifier  blocks the dc component of voltage and allows only the ac component to pass through it. The amplified ac signal was then fed to a HP spectrum analyser that  displayed  the  spectral  power  density  of  voltage  fluctuation  (Sv) as a function of frequency (f). For determining 1/f noise with frequency, we took the noise spectra with and without (consisting of preamplifier + thermal noise) current.  Then  the  latter  spectrum  was  subtracted  from  the  former,  and  we  obtained pure 1/f noise spectrum that was due to the conductivity fluctua-tions inside the sample. The background noise spectrum showed a 1/f contribu-tion arising from the preamplifier for frequencies < 5 Hz. Above 5 Hz, back-ground noise remains constant (frequency independent white noise). We could achieve a sensitivity of 2.5×10- 18 V 2/Hz at room temperature and 10 Hz.    Fig. 1 - 1/f noise measurement setup   In order to study the temperature variation, the sample was loaded in the cryostat. The temperature was varied between 80 K and 300 K using Lakeshore  340  temperature  controller.  Pt  -  100  sensor  was  used  for  detecting the temperature and cartridge heater was used for the heating purpose. Before taking the noise reading at any value, the temperature was stabilized within 10 mK.    678 ASHUTOSH KUMAR, ASHISH KUMAR, K. ASOKAN, ET AL.  3. RESULTS AND DISCUSSION  Contacts  play  an  important  role  in  1/f noise studies [5, 7] so it is very important to check the stability of contacts with in the temperature range in which 1/f noise investigation has to be done. So in order to check the stability of contacts, I-V measurements were done at various temperatures in the temperature range 80 K - 325 K. The straight line at each temperature ensures  that  contacts  were  ohmic.  I-V  at  different  temperatures  for  n-GaN  epitaxial layer grown on sapphire with indium contacts is shown in Fig. 2.    Fig. 2 - V-I at different temperatures   The variation in spectral power density of voltage fluctuations (Sy) with frequency (f) was observed at various temperatures in the frequency range 100  mHz  to  50  Hz.  The  variation  in  spectral  power  density  of  voltage  fluctuation with frequency at 80 K and 300 K is shown in Fig. 3. Theoretical 1/f line was also plotted. The deviation of the experimental results from the theoretical 1/f line  can be explained by Hooge Model  [1],  which states that spectral power density of voltage fluctuations (Sv) varies as 1/f γ and g varies between 0.8-1.2.    Fig. 3 - Spectral voltage noise density as a function of frequency at 80 K and 300 K  1/f noise is more at lower frequency side and it is due to presence of large number of traps having wide distribution of relaxation time and it is found that in semiconductors spectral power density becomes frequency dependent [3]. If t is the relaxation time for a trap, then spectral power density is given as   S (f) ~ 2t / (1 + (2pft) 2) (1)      TEMPERATURE DEPENDENCE OF 1/f NOISE IN… 679  At the lower frequency (f << 1/t,) S (f) = constant and at high frequency (f >> 1/t), S (f) ~ 1/f². In the presence of distribution of relaxation time, by averaging the spectrum at different relaxation time, we get 1/f spectrum [2].  At f = 10 Hz, the variation of spectral power density of voltage fluctuations (Sv) with temperature was observed and it is shown in Fig. 4. Sv was found to be slightly increasing with in temperature range 80-300 K. As temperature increases, more defects will become mobile and participate in the trapping-detrapping of charge carriers [4]. So fluctuation in the conductivity is more due to this trapping and detrapping process, spectral power density of voltage fluctuations increases.      Fig. 4 - Spectral voltage noise density as a function of temperature at f = 10 Hz  4. CONCLUSION  We have observed the 1/f variation of spectral noise voltage density with frequency at the lower frequency side (100-50 Hz). The origin of this type of noise in semiconductors is attributed to the presence of traps. The temperature variation of the noise is also investigated ant it is attributed to the  trapping-detrapping  process.  Contacts  plays  an  important  role  in  1/f noise studies so I-V was done at each temperature of the noise measurement and at each temperature, contacts were found to be ohmic.  Ashutosh  Kumar  is  grateful  to  the  Dr.  D.  Kanjilal  of  Inter  University  Accelerator  Centre,  New Delhi  for  his  support  during this  work.  Ashutosh Kumar is also thankful to CSIR for research fellowship.  REFERENCES 1. F.N. Hooge, IEEE T. Electron. Dev. 41, 1926 (1994). 2. A.K. Raychaudhari, Curr. Opin. Solid St. M. 67, 6 (2002). 3. L.K.J. Vandamme, X. Li, D. Rigaud, IEEE T. Electron Dev. 41, 1936 (1994). 4. H. Wong, Microelectron. Reliab. 43, 585 (2003). 5. B.H. Leung, W.K. Fong, C. Surya, Opt. Mat. 23, 203 (2003). 6. R. Singh, D. Kanjilal, J. Appl. Phys. 91, 411 (2002). 7. N. Tanuma, M. Tacano, J. Pavelka, S. Hashiguchi, J. Sikula, T. Matsui, Solid-State Electron. 49 865 (2005). 

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Temperature dependence of 1/f noise in Gallium Nitride epitaxial layer

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