Ag/p-Sn0.2Se0.8 Schottky barrier diodes have been fabricated and characterized by the current-voltage (I-V) technique as a function of temperature in the range of 303 K to 403 K. The forward bias characteristics have been analyzed on the basis of thermionic emission (TE) theory and the characteristic parameters of Schottky barrier diode such as barrier height, ideality factor and series resistance have been determined. The conventional Richardson plot was drawn and the value of Richardson constant was determined using the intersection of Ln(I0/T2) vs 1000/T. It is found to be around 15 Acm – 2K – 2 which is closer to the reported value for SnSe.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2212

Patel, K.D.

Patel, K.K.

Patel, M.

Pathak, V.M.

Solanki, G.K.

Srivastava, R.

Electronic Sumy State University Institutional Repository

   J. Nano- Electron. Phys. 3 (2011) No1, P. 783-786 Ó 2011 SumDU (Sumy State University)   783 PACS numbers: 73.40Ns. 73.30. + y, 73.40Ei, 73.90 + F  TEMPERATURE DEPENDENT I-V CHARACTERISTICS OF  Ag/p-Sn0.2Se0.8 THIN FILM SCHOTTKY BARRIER DIODE  K.K. Patel1, M. Patel2, K.D. Patel2, G.K. Solanki2, V.M. Pathak2,  R. Srivastava2  1 Smt. S. M. Panchal Science College,  Talod, 383215, Gujarat, India  E-mail: karm1962@gmail.com 2 Patel University,  Vallabh Vidyanagar, 388120, Gujarat, India  Ag/p-Sn0.2Se0.8 Schottky barrier diodes have been fabricated and characterized by the current-voltage (I-V) technique as a function of temperature in the range of 303 K to 403 K. The forward bias characteristics have been analyzed on the basis of thermionic emission (TE) theory and the characteristic parameters of Schottky barrier diode such as barrier height, ideality factor and series resistance have been determined. The conventional  Richardson plot  was drawn and the value of  Richardson constant was determined using the intersection of Ln(I0/T2) vs 1000/T. It is found to be around 15 Acm – 2K – 2 which is closer to the reported value for SnSe.  Keywords: SCHOTTKY DIODE, I-V CHARACTERISTICS, BARRIER HEIGHT, IDEALITY FACTOR, RICHARDSON PLOT.  (Received 04 February 2011)  1. INTRODUCTION  IV-VI group semiconductors can be categorized into rhombohedral, cubic and orthorhombic compounds. Tin selenide belongs to these group of compounds and has the layered orthorhombic structure [1, 2]. It has attracted conside-rable attention because of their important specific properties in the area of optoelectronics [3], holographic recording [4-6] and electronic switching [7-8]. Moreover SnSe is  a  semiconductor possessing a band gap of  about 1 eV and has a potential for an efficient solar cell material [3, 9]. Metal-semiconductor structures are important research tools in the characterization of semiconducting materials and fabrication of such type of structures  plays  an  important  role  in  the  realization  of  some  useful  devices [10]. Extraction of device parameters, measured only at room temperature, dose not provide enough information regarding conduction mechanism  and  the  nature  of  barrier  formation  at  the  M-S  interface.  The  characteristics measured over a wide temperature range provide the more satisfactory information for understanding the different aspects of conduction mechanisms  [11].  There  have  been  many  reports  on  study  of  I-V  characteristics and barrier parameters in case of semiconductors in bulk form but as per our knowledge no report could be found for such study in case of materials having off stoichiometric proportion. In present study, we report the forward bias I-V characteristics of Ag/p-Sn0.2Se0.8 Schottky barrier diode in the high temperature range of 303 K to 403 K and evaluation of barrier parameters.    784 K.K. PATEL, M. PATEL, K.D. PATEL, ET AL.  2. EXPERIMENTAL   To fabricate thin film Ag/p-Sn0.2Se0.8 Schottky  barrier  diodes  on  non  conductive glass substrates, the substrates were first cleaned by ultrasonic vibrations followed by thorough washing with detergent and acetone. Silver film of 6000 Å was deposited on glass substrate by thermal evaporation. Silver coated substrates were heated at 150 °C for providing better adhesion of  subsequent  films.  Using  proper  mask  Sn0.2Se0.8 films of thickness 10000 Å and 0.175 cm2 area were deposited by flash evaporation on the silver coated substrates at room temperature. Here flash evaporation technique has been used to maintain the stoichiometric proportion. For this purpose Sn0.2Se0.8 charge in powder form was prepared by reacting highly pure Sn (99.9+), Se (99.9+) powder taken in required proportion heated at proper temperature in evacuated and sealed quartz ampoule. The chemical composition of deposited Sn0.2Se0.8 thin  films  was  confirmed  by  EDAX  analysis.  Ohmic  contacts  on  Sn0.2Se0.8 films were obtained by depositing indium films of 10000 Å. All these depositions were carried out in a residual pressure of 10 – 6 torr. External contacts from In and Ag were taken using adhesive and conducting silver paste (Elteck-1228C) through copper wires. The I-V measurements were performed in the temperature range 303 K to 403 K using specially designed sample holder with inbuilt heater and semiconductor characterization system- Keithley 4200 under dark conditions.  3. RESULTS AND DISCUSSION  The obtained I-V plots of fabricated Schottky diode are shown in fig. 1a. These show that the fabricated diodes exhibit good rectification nature with rectification ratio of 464 at ± 2 V. According to TE theory I-V relationship of a Schottky barrier diode is given by [12]   = - -0 exp( )[1 exp( )]qV qVI InkT kT (1)  where    2 00 exp[ ]bqI AA TkTf*= -  (2)  Here I0 is the saturation current, V is  the  forward-bias  voltage,  k  is  Boltzmann constant, q is electronic charge, A is the diode area, T is absolute temperature, A* is the effective Richardson constant having the value  18 cm – 2K – 2 for  SnSe [13].  The zero-bias  barrier  height (fb0) and ideality factor ( ) from equation (1) can be written as   20*ln( )bokT AA Tq If =  (4)   (ln )q dVnkT d I=    The flat band barrier height can be calculated using the following equation     TEMPERATURE DEPENDENT I-V CHARACTERISTICS OF… 785  ( ) ln [ ]Vbf bANkTn nq Nf f 0= - - 1  (5)  where Nv and NA are effective density of states in valance band and carrier concentration. The values of f, fb0 and fbf were determined from the intercept and slope of the ln I-V plot (Fig. 1b) for forward bias. These values of fb0, f and fbf obtained from equation (3), (4) and (5) have been plotted as a function of temperature in Fig. 2a.     a b   Fig. 1 – I-V Characteristics of Ag/p-Sn0.2Se0.8 SBD (a), and Ln I vs V plot for Ag/p-Sn0.2Se0.8 SBD (b)    (a)              (b)   Fig. 2 – Variation of barrier heights and ideality factor with Temperature (a) Conventional Richardson plot (b)  It is seen from here that in flat band barrier height and ideality factor decrease sharply in the initial part of 303-330 K and after that they found to become constant. At the same time the value of zero bias barrier height increases slowly with temperature attaining a value around 1.0 eV (Fig. 2a). Since current transport across the MS interface is a temperature activated process, electrons at low temperatures are able to surmount the lower barriers and therefore current transport will be dominated by current    786 K.K. PATEL, M. PATEL, K.D. PATEL, ET AL.  flowing through patches of the lower Schottky barrier heights (SBH) accounting for the larger ideality factor for observed values [14]. As the temperature increases, more and more electrons are likely to have sufficient energy to surmount even larger barriers. As a result, the dominant barrier height will increase with the temperature and bias voltage. Equation (2) can be rearranged as   02ln[ ] ln( *)qIAAkTTf¶= -  (6)  It is known as the Richardson equation. Based on this equation a plot of ln  (I0/T2) vs. 1000/T were drawn (fig. 2b). The plot should be a straight line.  The  value  of  Richardson  constant  obtained  from  this  plot  is  around  15 Acm – 2K – 2,  this  can  be  compared  to18  Acm – 2K – 2 for  SnSe.  The  deviation in Richardson plot may be due to high ideality factor, high series resistance (47 kW to 467 kW) and deviation in composition from SnSe.  4. CONCLUSION   Ag/p-Sn0.2Se0.8 Schottky diodes have been fabricated and studied in the temperature range of 303 K – 403 K for their I-V characteristics.  These characteristics show good rectification ratio at RT (464 at ± 2 V). The zero bias barrier height increases while the flat band barrier height and ideality factor  decreases with the temperaure. The value of Richardson constant as determined from the Richardson plot without considering the contributions due to inhomogeneous barrier, is found to be around 15 Acm – 2K – 2.  We are thankful to UGC for financial assistance in the form of teacher fellowship and major research project.  REFERENCES 1. G. Lucovsky, R.M. Martin, E. Burstain, Conf. on Physics of IV-VI compounds and Alloys (Uni. Of Pennsylvania: Philadelphia P. A.: 1972). 2. G. Valiukonis, D.A. Guseinova, G. Krivaite, A. Sileika, phys. status solidi B 135, 299 (1986). 3.  M. Parentau, M. Carlone, Phys. Rev. B 41, 5227 (1990). 4. D.J. Bletskan, V.I. Taran, M.Yu. Sichka, Ukr. J. Phys. 21, 1436 (1976). 5. J.P. Shing, R.K. Bedi, J. Appl. Phys. 68, 2776 (1990). 6. R.K. Bedi, B.S.V. Gopalan, J. Majhi, Conference  on  Physics  and  Technology  of  Semiconductor devices and integrated circuites, SPIE Publications, 104 (1992). 7. J.J. Lofersky, J. Appl. Phys. 27, 777 (1956). 8. J.J. Lofersky, Proc. IEEE 51, 667 (1963). 9. M. Rodot, Rev. Phys. Appl. 12, 411 (1977). 10. N. Tugluoglu, S. Karadeniz, M. Sahin, H. Safak, Appl. Surf. Sci. 233, 320 (2004). 11. A.J. Mathai, K.D. Patel, R. Srivastava, Thin Solid Films 518, 4417 (2010). 12. E.H. Rhoderic, and R.H. Williams, Metal Semiconductor Contacts, 2nd edn. (Oxford: Clarendon). 13. N. Tugluoglu, S. karadeniz, M. Sahin, H. Safak, Semicond. Sci. Technol. 19(9), 1092 (2004). 14. M.K. Hudait, P. Venkatswarlu, S.B. Kraupanidhi, Solid. State Electron. 45, 133 (2001). 

Temperature dependent I-V characteristics of Ag/p-Sn0.2Se0.8 thin film Schottky barrier diode

SocioEconomic Challenges Journal (Sumy State University)

 
 
 
J. Nano- Electron. Phys. 
3 (2011) No1, P. 783-786 
Ó 2011 SumDU 
(Sumy State University) 
 
 
783 
PACS numbers: 73.40Ns. 73.30. + y, 73.40Ei, 73.90 + F 
 
TEMPERATURE DEPENDENT I-V CHARACTERISTICS OF  
Ag/p-Sn0.2Se0.8 THIN FILM SCHOTTKY BARRIER DIODE 
 
K.K. Patel1, M. Patel2, K.D. Patel2, G.K. Solanki2, V.M. Pathak2,  
R. Srivastava2 
 
1 Smt. S. M. Panchal Science College, 
 Talod, 383215, Gujarat, India 
 E-mail: karm1962@gmail.com 
2 Patel University, 
 Vallabh Vidyanagar, 388120, Gujarat, India 
 
Ag/p-Sn0.2Se0.8 Schottky barrier diodes have been fabricated and characterized by the 
current-voltage (I-V) technique as a function of temperature in the range of 303 K to 
403 K. The forward bias characteristics have been analyzed on the basis of thermionic 
emission (TE) theory and the characteristic parameters of Schottky barrier diode 
such as barrier height, ideality factor and series resistance have been determined. The 
conventional  Richardson plot  was drawn and the value of  Richardson constant was 
determined using the intersection of Ln(I0/T2) vs 1000/T. It is found to be around 
15 Acm – 2K – 2 which is closer to the reported value for SnSe. 
 
Keywords: SCHOTTKY DIODE, I-V CHARACTERISTICS, BARRIER HEIGHT, 
IDEALITY FACTOR, RICHARDSON PLOT. 
 
(Received 04 February 2011) 
 
1. INTRODUCTION 
 
IV-VI group semiconductors can be categorized into rhombohedral, cubic and 
orthorhombic compounds. Tin selenide belongs to these group of compounds 
and has the layered orthorhombic structure [1, 2]. It has attracted conside-
rable attention because of their important specific properties in the area of 
optoelectronics [3], holographic recording [4-6] and electronic switching [7-8]. 
Moreover SnSe is  a  semiconductor possessing a band gap of  about 1 eV and 
has a potential for an efficient solar cell material [3, 9]. 
Metal-semiconductor structures are important research tools in the 
characterization of semiconducting materials and fabrication of such type of 
structures  plays  an  important  role  in  the  realization  of  some  useful  
devices [10]. Extraction of device parameters, measured only at room 
temperature, dose not provide enough information regarding conduction 
mechanism  and  the  nature  of  barrier  formation  at  the  M-S  interface.  The  
characteristics measured over a wide temperature range provide the more 
satisfactory information for understanding the different aspects of conduction 
mechanisms  [11].  There  have  been  many  reports  on  study  of  I-V  
characteristics and barrier parameters in case of semiconductors in bulk form 
but as per our knowledge no report could be found for such study in case of 
materials having off stoichiometric proportion. 
In present study, we report the forward bias I-V characteristics of Ag/p-
Sn0.2Se0.8 Schottky barrier diode in the high temperature range of 303 K to 
403 K and evaluation of barrier parameters. 
 
 
 
784 K.K. PATEL, M. PATEL, K.D. PATEL, ET AL.  
2. EXPERIMENTAL  
 
To fabricate thin film Ag/p-Sn0.2Se0.8 Schottky  barrier  diodes  on  non  
conductive glass substrates, the substrates were first cleaned by ultrasonic 
vibrations followed by thorough washing with detergent and acetone. Silver 
film of 6000 Å was deposited on glass substrate by thermal evaporation. 
Silver coated substrates were heated at 150 °C for providing better adhesion 
of  subsequent  films.  Using  proper  mask  Sn0.2Se0.8 films of thickness 
10000 Å and 0.175 cm2 area were deposited by flash evaporation on the 
silver coated substrates at room temperature. Here flash evaporation 
technique has been used to maintain the stoichiometric proportion. For this 
purpose Sn0.2Se0.8 charge in powder form was prepared by reacting highly 
pure Sn (99.9+), Se (99.9+) powder taken in required proportion heated at 
proper temperature in evacuated and sealed quartz ampoule. The chemical 
composition of deposited Sn0.2Se0.8 thin  films  was  confirmed  by  EDAX  
analysis.  Ohmic  contacts  on  Sn0.2Se0.8 films were obtained by depositing 
indium films of 10000 Å. All these depositions were carried out in a residual 
pressure of 10 – 6 torr. External contacts from In and Ag were taken using 
adhesive and conducting silver paste (Elteck-1228C) through copper wires. 
The I-V measurements were performed in the temperature range 303 K to 
403 K using specially designed sample holder with inbuilt heater and 
semiconductor characterization system- Keithley 4200 under dark conditions. 
 
3. RESULTS AND DISCUSSION 
 
The obtained I-V plots of fabricated Schottky diode are shown in fig. 1a. 
These show that the fabricated diodes exhibit good rectification nature with 
rectification ratio of 464 at ± 2 V. 
According to TE theory I-V relationship of a Schottky barrier diode is 
given by [12] 
 
 = - -0 exp( )[1 exp( )]
qV qV
I I
nkT kT
 (1) 
 
where  
 
 2 00 exp[ ]
bqI AA T
kT
f*= -  (2) 
 
Here I0 is the saturation current, V is  the  forward-bias  voltage,  k  is  
Boltzmann constant, q is electronic charge, A is the diode area, T is absolute 
temperature, A* is the effective Richardson constant having the value  
18 cm – 2K – 2 for  SnSe [13].  The zero-bias  barrier  height (fb0) and ideality 
factor ( ) from equation (1) can be written as 
 
 
2
0
*
ln( )bo
kT AA T
q I
f =  (4) 
 
 
(ln )
q dV
n
kT d I
=   
 
The flat band barrier height can be calculated using the following equation 
 
 
 
 TEMPERATURE DEPENDENT I-V CHARACTERISTICS OF… 785 
 ( ) ln [ ]Vbf b
A
NkT
n n
q N
f f 0= - - 1  (5) 
 
where Nv and NA are effective density of states in valance band and carrier 
concentration. The values of f, fb0 and fbf were determined from the 
intercept and slope of the ln I-V plot (Fig. 1b) for forward bias. These values 
of fb0, f and fbf obtained from equation (3), (4) and (5) have been plotted as 
a function of temperature in Fig. 2a. 
 
  
 a b  
 
Fig. 1 – I-V Characteristics of Ag/p-Sn0.2Se0.8 SBD (a), and Ln I vs V plot for Ag/p-
Sn0.2Se0.8 SBD (b) 
 
  
(a)              (b)  
 
Fig. 2 – Variation of barrier heights and ideality factor with Temperature (a) 
Conventional Richardson plot (b) 
 
It is seen from here that in flat band barrier height and ideality factor 
decrease sharply in the initial part of 303-330 K and after that they found 
to become constant. At the same time the value of zero bias barrier height 
increases slowly with temperature attaining a value around 1.0 eV (Fig. 2a). 
Since current transport across the MS interface is a temperature activated 
process, electrons at low temperatures are able to surmount the lower 
barriers and therefore current transport will be dominated by current 
 
 
 
786 K.K. PATEL, M. PATEL, K.D. PATEL, ET AL.  
flowing through patches of the lower Schottky barrier heights (SBH) 
accounting for the larger ideality factor for observed values [14]. As the 
temperature increases, more and more electrons are likely to have sufficient 
energy to surmount even larger barriers. As a result, the dominant barrier 
height will increase with the temperature and bias voltage. 
Equation (2) can be rearranged as 
 
 0
2
ln[ ] ln( *)
qI
AA
kTT
f¶= -  (6) 
 
It is known as the Richardson equation. Based on this equation a plot of 
ln  (I0/T2) vs. 1000/T were drawn (fig. 2b). The plot should be a straight 
line.  The  value  of  Richardson  constant  obtained  from  this  plot  is  around  
15 Acm – 2K – 2,  this  can  be  compared  to18  Acm – 2K – 2 for  SnSe.  The  
deviation in Richardson plot may be due to high ideality factor, high series 
resistance (47 kW to 467 kW) and deviation in composition from SnSe. 
 
4. CONCLUSION  
 
Ag/p-Sn0.2Se0.8 Schottky diodes have been fabricated and studied in the 
temperature range of 303 K – 403 K for their I-V characteristics.  These 
characteristics show good rectification ratio at RT (464 at ± 2 V). The zero 
bias barrier height increases while the flat band barrier height and ideality 
factor  decreases with the temperaure. The value of Richardson constant as 
determined from the Richardson plot without considering the contributions 
due to inhomogeneous barrier, is found to be around 15 Acm – 2K – 2. 
 
We are thankful to UGC for financial assistance in the form of teacher 
fellowship and major research project. 
 
REFERENCES 
1. G. Lucovsky, R.M. Martin, E. Burstain, Conf. on Physics of IV-VI compounds and 
Alloys (Uni. Of Pennsylvania: Philadelphia P. A.: 1972). 
2. G. Valiukonis, D.A. Guseinova, G. Krivaite, A. Sileika, phys. status solidi B 135, 
299 (1986). 
3.  M. Parentau, M. Carlone, Phys. Rev. B 41, 5227 (1990). 
4. D.J. Bletskan, V.I. Taran, M.Yu. Sichka, Ukr. J. Phys. 21, 1436 (1976). 
5. J.P. Shing, R.K. Bedi, J. Appl. Phys. 68, 2776 (1990). 
6. R.K. Bedi, B.S.V. Gopalan, J. Majhi, Conference  on  Physics  and  Technology  of  
Semiconductor devices and integrated circuites, SPIE Publications, 104 (1992). 
7. J.J. Lofersky, J. Appl. Phys. 27, 777 (1956). 
8. J.J. Lofersky, Proc. IEEE 51, 667 (1963). 
9. M. Rodot, Rev. Phys. Appl. 12, 411 (1977). 
10. N. Tugluoglu, S. Karadeniz, M. Sahin, H. Safak, Appl. Surf. Sci. 233, 320 (2004). 
11. A.J. Mathai, K.D. Patel, R. Srivastava, Thin Solid Films 518, 4417 (2010). 
12. E.H. Rhoderic, and R.H. Williams, Metal Semiconductor Contacts, 2nd edn. 
(Oxford: Clarendon). 
13. N. Tugluoglu, S. karadeniz, M. Sahin, H. Safak, Semicond. Sci. Technol. 19(9), 
1092 (2004). 
14. M.K. Hudait, P. Venkatswarlu, S.B. Kraupanidhi, Solid. State Electron. 45, 133 
(2001). 


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Temperature dependent I-V characteristics of Ag/p-Sn0.2Se0.8 thin film Schottky barrier diode

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