Investigation and understanding of Schottky diodes continue to be interesting both for basic as well as technological points of view. Even now the evolutionary aspects of such contacts are not very clearly understood. In this paper it is shown that in respect of interfacial strain contribution to the barrier heights of such contacts semiconductor – liquid metal contacts are relatively better placed than solid semiconductor-solid metal contacts. Results on Ga-Si(p) contact are discussed in this paper to show phase sensitive contribution to the barrier height of such Schottky contacts.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3099

Dhimmar, J.M.

Modi, B.P.

Patel, K.D.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02005(3pp) (2013) Том 5 № 2, 02005(3cc) (2013) 
 
2077-6772/2013/5(2)02005(3) 02005-1  2013 Sumy State University 
Phase Transition Sensitive Schottky Barriers In Ga-Si(P) Contacts 
 
B.P. Modi1,*, J.M. Dhimmar1, K.D. Patel2 
 
1 Department of Physics, Veer Narmad South Gujarat University, Surat-395 007,Gujarat, India 
2 Departments of Physics, Sardar Patel University. Vallabhvidyanagar-388 120, Gujarat, India  
 
(Received 15 February 2013; revised manuscript received 03 May 2013; published online 04 May 2013) 
 
Investigation and understanding of Schottky diodes continue to be interesting both for basic as well as 
technological points of view. Even now the evolutionary aspects of such contacts are not very clearly  
understood. In this paper it is shown that in respect of interfacial strain contribution to the barrier heights 
of such contacts semiconductor – liquid metal contacts are relatively better placed than solid semiconduc-
tor-solid metal contacts. Results on Ga-Si(p) contact are discussed in this paper to show phase sensitive 
contribution to the barrier height of such Schottky contacts. 
 
Keywords: Schottky barrier, Phase transition, Barrier height, Ideality factor. 
 
 PACS numbers: 73.30. + y, 73.20. – r 
 
 
                                                 
* bharatpmodi.bharuch@gmail.com 
1. INTRODUCTION 
 
Metal-semiconductor (M-S) contacts have continued 
as an important and interesting field for investigations 
both from points of view of science and technology [1, 2]. 
In comparison to solid-solid M-S contacts, relatively few-
er investigations have been reported for liquid metal 
semiconductor contacts. In earlier paper [3, 4] we had 
reported advantages of investigations on such contacts 
along with the results of our studies on stability aspects 
of such contacts of Schottky nature. It was shown that 
these contacts are fairly stable in their behaviour over a 
long period of time and thus show negligible ageing ef-
fect. Hence, these make themselves as suitable systems 
for closely looking at the evolutionary aspects of Schottky 
contacts. Here in this paper, we report results of our in-
vestigations on Schottky contacts between liquid gallium 
and silicon, especially around the melting point of galli-
um. It is shown that such contacts exhibit a phase transi-
tion sensitive characteristics around the melting point, 
driven by the interfacial strain. Imprint of this are seen 
in both I-V-T and C-V-T characteristics of such contacts. 
 
2. EXPERIMENTAL 
 
In this investigation p-type Si <100> crystals ha-
ving acceptor density of around 1016 /cm3 were used. 
The ohmic back contact on the rough surface of the sili-
con crystal was made of aluminium by depositing 
0.15 m thick film of pure aluminium by thermal evap-
oration in a vacuum of around 10 – 6 torr followed by 
thermal annealing at 500 C for half an hour. The other 
polished surface of the crystal was etched in 1 : 3 : 5 
mixture of electronic grade hydrofluoric acid, nitric acid 
and acetic acid for around 30 seconds when brown va-
pors appeared and then it was dipped for a minute in 
dilute solution of 1 : 9 hydrofluoric acid and deionised 
water. Finally it was thoroughly washed in deionized 
water and quickly dried. The crystal was then mounted 
in the sample holder [5] below the capillary arrange-
ment and pure gallium (99.99 %) was put into the capil-
lary using a disposable syringe. The I-V data on the 
formed Schottky diodes were obtained at 100 Hz and  
C-V data were obtained at 100 kHz using HP-LCR me-
ter (Model-4274A) through a suitably developed soft-
ware programme. The choice of 100 Hz for I-V data was 
made so that characteristics are near dc behavior and 
choice of 100 kHz for C-V data was made so that any 
interfacial capacitance due to interface charges etc. does 
not contribute significantly. Temperature variations 
were made by controlling the ambient room tempera-
ture of the AC room, housing the experimental ar-
rangement, since the range of temperature variation for 
the present study is ten degrees only around the room 
temperature. The temperature near the Schottky con-
tact was measured using a suitably placed thermometer 
with an accuracy of  0.10 C. 
 
3. RESULTS AND DISCUSSIONS 
 
The I-V data on the Schottky contact at different 
temperatures (295 K, 297 K, 299 K, 302 K and 305 K) 
are shown in Fig. 1. From this figure, it can be observed 
that I-V characteristics of the Schottky contact around 
the melting point of gallium(302.750 K) is anomalous in 
the sense that there is a sharp deterioration in the rec-
tifying nature near this temperature. 
 
-0.0002
-0.0001
0
0.0001
0.0002
0.0003
0.0004
0.0005
-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8
I 
(A
)
V (volt)
T=295
K
T=297
K
T=299
K
T=302
K
 
 
Fig. 1 – I-V characteristics of Ga-Si(p) diode at different tem-
perature around melting point of  gallium 
 B.P. MODI, J.M. DHIMMAR, K.D. PATEL J. NANO- ELECTRON. PHYS. 5, 02005 (2013) 
 
 
02005-2 
Otherwise, the rectification behavior at other tem-
peratures is quite good. To highlight this and to see 
this more closely, both forward and reverse bias data 
have been plotted as a function of temperature at some 
fixed but different values of forward and reverse biases. 
These are shown in Fig. 2. The anomalous behaviour 
around the melting point of gallium is quite prominent-
ly exhibited by this figure and is seen to be centered in 
a narrow temperature region around the melting point 
of gallium (302.75 K). 
 
-0.0001
-0.00008
-0.00006
-0.00004
-0.00002
0
0.00002
0.00004
0.00006
0.00008
0.0001
294 296 298 300 302 304 306
I(A)
T(K)
-0.2 volt
-0.3 volt
-0.4 volt
-0.5 volt
-0.6 volt
-0.7 volt
-0.8 volt
-0.9 volt
-1.0 volt
0.1 volt
0.2 volt
0.3 volt
0.4 volt
0.5 volt
 
 
Fig. 2 – I-T Characteristics of Ga-Si(p) Schottky diode at dif-
ferent voltages before correction 
 
The equivalent circuit of a practical Schottky diode 
generally includes a series and a shunt resistance be-
sides a capacitance in parallel to the junction. The pres-
ence of series and shunt resistances can affect the meas-
ured I-V data as pointed in our earlier paper [3]. There-
fore, more realistic I-V characteristics were obtained 
after corrections made as discussed earlier and the re-
sulting I-T characteristics at different biases is shown in 
Fig. 3. This shows that the observed anomaly is true one 
in the present case although its observed magnitude is 
reduced by presence of these parasitic components. 
 
-0.0001
-0.00008
-0.00006
-0.00004
-0.00002
0
0.00002
0.00004
0.00006
0.00008
0.0001
294 295 296 297 298 299 300 301 302 303 304 305 306
I (A)
T (K)
-
.3
V
-
.6
V
-
.9
V
 
Fig. 3 – I-T Characteristics of Ga-Si(p) Schottky diode 
at different voltages after correction 
 
The C-V-T data obtained on the Schottky contact was 
plotted (Fig. 4) to show variation of capacitance with 
temperature at fixed biases. From here it can be seen 
that there is significant change in the trend of varia-
tion in the magnitude of exhibited capacitance values. 
0
2E-10
4E-10
6E-10
8E-10
1E-09
1.2E-09
1.4E-09
296 298 300 302 304 306 308 310
Capacitanc
e (F)
T (K)
V=-0.5
volt
V=-1.0
volt
V=-1.5
volt
 
Fig. 4 – Capacitance vs Temperature of Ga-Si (p) Schottky 
diode at different voltages  
 
To make it more apparent, the rate of change of capaci-
tance values at these different fixed biases were plot-
ted. This is shown in Fig. 5. It is seen that a similar 
kind of anomaly as seen in current voltage characteris-
tics around melting point of gallium is also visible in 
the capacitance voltage characteristics. 
 
0
5E-12
1E-11
1.5E-11
2E-11
2.5E-11
296 298 300 302 304 306 308 310
[dC/dT] 
(F/K)
T (K)
V= -
V= -1.0 V
V= -2.0 V
 
 
Fig. 5 – (dC) / (dT) (F / K) vs Temperature of Ga-Si(p) Schott-
ky diode at different voltages 
 
I-V-T and C-V-T behaviour of Schottky contacts 
originate from interfacial dipole layer characteristics 
and charge transport mechanisms through it [6]. As far 
as charge transport in the present case is concerned, it 
is thermionic emission. Such an inference is based on: 
 the doping density in the semiconductor used (sili-
con in the present case) is not high and the tempera-
ture at which characteristics are being observed is not 
very low to warrant tunneling as the dominating 
charge transport mechanism,  
 the characteristics energy E00, as calculated in pre-
sent case, is not of the order of kT to warrant thermionic 
field emission as dominant charge transport mechanism. 
On the contrary E00 is more than ten orders lower than 
kT as required for identifying ther-mionic emission as 
dominant charge transport mechanism. 
Analyzing the observed behaviour on such basis 
shows that the ideality factor is around 1.1 at all tem-
peratures. However, the flat band barrier height and 
built in potential show a decrease near the melting 
point of gallium Fig. 6. 
 PHASE TRANSITION SENSITIVE SCHOTTKY BARRIERS … J. NANO- ELECTRON. PHYS. 5, 02005 (2013) 
 
 
02005-3 
0.78
0.8
0.82
0.84
0.86
0.88
0.9
0.92
0.94
290 295 300 305 310
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
290 295 300 305 310
B
u
ilt in
 p
o
te
n
tia
l (e
V
)
F
la
t 
B
a
n
d
 B
a
rr
ie
r 
H
e
ig
h
t 
(e
V
)
Temperature K
Flat Band barrier height
(eV)
 
 
Fig. 6 – Flat band barrier height and built-in volt potential 
variation with temperature for Ga-Si(p) diode 
 
It has been reported in the literature [7-9] that the 
Schottky diode behaviour in general have contributions 
both from the bulk materials used in the contact as well 
as their interface. Therefore, it can be thought that the 
observed anomaly around the phase transition of galli-
um is driven by changes in the bulk properties of galli-
um or its interface with silicon, since the bulk properties 
of silicon are not expected to show any significant change 
around this temperature. Moreover, the contact with 
liquid gallium has been made immediately on the 
cleaned and etched silicon surface leaving little time for 
formation of oxide layer of any significant thickness. 
Melting/solidification of a substance is a phase 
transition of the first kind. It is seen that in such phase 
transitions there is a rearrangement of crystal lattice of 
the substance consisting of changes in the interatomic 
distances and the angle between lattice planes. As a 
result the symmetry of the substance changes discon-
tinuously. At the same time there is a discontinuous 
change in the volume and density as well. There is also 
a change in the internal energy accompanied by evolu-
tion or absorption of heat energy, which is known as 
latent heat of transition and does not appear as an  
apparent change in the temperature of the substance. 
All this occurs over a narrow range of temperature cen-
tered on the phase transition temperature. The ther-
modynamic conditions of equilibrium for these kinds of 
discontinuous changes between phases of different 
symmetry require that such transitions occur at con-
stant temperature and pressure. But in processes oc-
curring at constant pressure the quantity of heat ab-
sorbed by the body is equal to change in its heat func-
tion and consequently the entropy also undergoes a 
change during such phase transitions. Analyzing the 
effect of this kind of changes in the internal energy of 
bulk gallium on the saturation current and consequent-
ly on the barrier height, it is found that it is negligible 
as compared to the observed changes. This is also certi-
fied by the fact that no anomalous change in the resis-
tivity of gallium has been reported around the melting 
point of gallium [10]. Moreover, it has also been report-
ed that structural disturbances set-in very slowly in 
gallium on melting. It has also been reported [11] from 
the structure-factor variation study across the melting 
point of gallium that the number of nearest neighbors 
and the sphere of first coordination remain almost un-
changed over a temperature range of 203 K to 323 K. 
Therefore, it seems that the observed anomaly origi-
nates predominantly from changes at the interface 
around the melting point of gallium and not from 
changes in the bulk properties of gallium. It may be 
noted that in case of solid-solid interface Schottky di-
odes, the contribution from interface is usually masked 
by the contributions from the bulk unless the thickness 
of metallic over layer coverage is few mono layers only. 
Exceptions to this have been reported rarely [7, 8]. 
Interfacial changes near the phase transition tem-
perature are likely to give rise to build up or relaxation 
of bonds between gallium and silicon – while silicon 
has cubic structure, gallium in the solid state has or-
thorhombic structure [12, 13]. Thus, interfacial strain 
can be expected to give rise to interface states and their 
additional creation may modify Fermi levels at the in-
terface, interfacial band alignment and the barrier 
height [14-16]. Obviously, the quantum of changes in 
the barrier height may be expected to depend on both 
the density of original interface states existing on the 
semiconductor and the density of interface states aris-
ing from interfacial strain. Therefore it can be conclud-
ed that the  evolutionary aspects of Schottky diodes e.g. 
contribution of interfacial strain which are seen only at 
smaller thicknesses of metallic over layers in case of 
solid-solid contacts may be seen more clearly in case of 
solid-liquid contacts.  
 
 
REFERENCES 
 
1. B.L. Sharma, Metal-Semiconductor Schottky Barrier Junc-
tions and Their Applications (Plennum Press: New York 
and London: 1984). 
2. V. Podzorov, M.E. Gershenson, Appl. Phys. Lett. 84, 3301 
(2004). 
3. B.P. Modi, J.M. Achamma, K.D. Patel, V.M. Pathak, 
R. Srivastava, Indian J. Pure Appl. Phys. 43, 184 (2005). 
4. J.M. Achamma, K.D. Patel, R. Srivastava, Thin Solid 
Films 518, 2695 (2010). 
5. K.D. Patel, Ph.D. thesis, Sardar Patel University, (1997). 
6. E.H. Rhoderick, Metal-Semiconductor contacts (Clarendon 
Press: Oxford, UK: 1978). 
7. G. Margaritindo, Rep. Prog. Phys. 62, 765 (1999). 
8. U. Rau, H.H. Guttler, J.H. Werner, MRS Proc. 260, 245 (1992). 
9. P. Perfetti, Surf. Rev. Lett. 2, 643 (1995). 
10. M. Pokorny, H.U. Astrom, J. Phys. F: Met. Phys. 6, 559 
(1976). 
11. M.P. Bharat, Ph D thesis, Sardar Patel University, (2003). 
12. W.F. McClune, Powder Diffraction file JCP DS(1983) 
13. J. Wolny, S. Niziol, W. Luznu, L. Pytlik, J. Soltys, 
R. Kokoszka, Solid State Commun. 58, 573 (1986). 
14. Mustafa Okutan, Engin Basaran, Faherttin Yaku-
phanoglu, Appl. Surf. Sci. 252, 1966 (2005).  
15. R.K. Mamoadov, M.A. Yeganesh, Microelectron. Reliab. 
52, 418 (2012). 
16. Ashish Kumar, Seema Vinayak, R. Singh, J. Nano-  
Electron. Phys. 3 No1, 671 (2011). 
 


English

Phase Transition Sensitive Schottky Barriers In Ga-Si(P) Contacts

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 2, 02005(3pp) (2013) Том 5 № 2, 02005(3cc) (2013)  2077-6772/2013/5(2)02005(3) 02005-1  2013 Sumy State University Phase Transition Sensitive Schottky Barriers In Ga-Si(P) Contacts  B.P. Modi1,*, J.M. Dhimmar1, K.D. Patel2  1 Department of Physics, Veer Narmad South Gujarat University, Surat-395 007,Gujarat, India 2 Departments of Physics, Sardar Patel University. Vallabhvidyanagar-388 120, Gujarat, India   (Received 15 February 2013; revised manuscript received 03 May 2013; published online 04 May 2013)  Investigation and understanding of Schottky diodes continue to be interesting both for basic as well as technological points of view. Even now the evolutionary aspects of such contacts are not very clearly  understood. In this paper it is shown that in respect of interfacial strain contribution to the barrier heights of such contacts semiconductor – liquid metal contacts are relatively better placed than solid semiconduc-tor-solid metal contacts. Results on Ga-Si(p) contact are discussed in this paper to show phase sensitive contribution to the barrier height of such Schottky contacts.  Keywords: Schottky barrier, Phase transition, Barrier height, Ideality factor.   PACS numbers: 73.30. + y, 73.20. – r                                                    * bharatpmodi.bharuch@gmail.com 1. INTRODUCTION  Metal-semiconductor (M-S) contacts have continued as an important and interesting field for investigations both from points of view of science and technology [1, 2]. In comparison to solid-solid M-S contacts, relatively few-er investigations have been reported for liquid metal semiconductor contacts. In earlier paper [3, 4] we had reported advantages of investigations on such contacts along with the results of our studies on stability aspects of such contacts of Schottky nature. It was shown that these contacts are fairly stable in their behaviour over a long period of time and thus show negligible ageing ef-fect. Hence, these make themselves as suitable systems for closely looking at the evolutionary aspects of Schottky contacts. Here in this paper, we report results of our in-vestigations on Schottky contacts between liquid gallium and silicon, especially around the melting point of galli-um. It is shown that such contacts exhibit a phase transi-tion sensitive characteristics around the melting point, driven by the interfacial strain. Imprint of this are seen in both I-V-T and C-V-T characteristics of such contacts.  2. EXPERIMENTAL  In this investigation p-type Si <100> crystals ha-ving acceptor density of around 1016 /cm3 were used. The ohmic back contact on the rough surface of the sili-con crystal was made of aluminium by depositing 0.15 m thick film of pure aluminium by thermal evap-oration in a vacuum of around 10 – 6 torr followed by thermal annealing at 500 C for half an hour. The other polished surface of the crystal was etched in 1 : 3 : 5 mixture of electronic grade hydrofluoric acid, nitric acid and acetic acid for around 30 seconds when brown va-pors appeared and then it was dipped for a minute in dilute solution of 1 : 9 hydrofluoric acid and deionised water. Finally it was thoroughly washed in deionized water and quickly dried. The crystal was then mounted in the sample holder [5] below the capillary arrange-ment and pure gallium (99.99 %) was put into the capil-lary using a disposable syringe. The I-V data on the formed Schottky diodes were obtained at 100 Hz and  C-V data were obtained at 100 kHz using HP-LCR me-ter (Model-4274A) through a suitably developed soft-ware programme. The choice of 100 Hz for I-V data was made so that characteristics are near dc behavior and choice of 100 kHz for C-V data was made so that any interfacial capacitance due to interface charges etc. does not contribute significantly. Temperature variations were made by controlling the ambient room tempera-ture of the AC room, housing the experimental ar-rangement, since the range of temperature variation for the present study is ten degrees only around the room temperature. The temperature near the Schottky con-tact was measured using a suitably placed thermometer with an accuracy of  0.10 C.  3. RESULTS AND DISCUSSIONS  The I-V data on the Schottky contact at different temperatures (295 K, 297 K, 299 K, 302 K and 305 K) are shown in Fig. 1. From this figure, it can be observed that I-V characteristics of the Schottky contact around the melting point of gallium(302.750 K) is anomalous in the sense that there is a sharp deterioration in the rec-tifying nature near this temperature.  -0.0002-0.000100.00010.00020.00030.00040.0005-2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8I (A)V (volt)T=295KT=297KT=299KT=302K  Fig. 1 – I-V characteristics of Ga-Si(p) diode at different tem-perature around melting point of  gallium  B.P. MODI, J.M. DHIMMAR, K.D. PATEL J. NANO- ELECTRON. PHYS. 5, 02005 (2013)   02005-2 Otherwise, the rectification behavior at other tem-peratures is quite good. To highlight this and to see this more closely, both forward and reverse bias data have been plotted as a function of temperature at some fixed but different values of forward and reverse biases. These are shown in Fig. 2. The anomalous behaviour around the melting point of gallium is quite prominent-ly exhibited by this figure and is seen to be centered in a narrow temperature region around the melting point of gallium (302.75 K).  -0.0001-0.00008-0.00006-0.00004-0.0000200.000020.000040.000060.000080.0001294 296 298 300 302 304 306I(A)T(K)-0.2 volt-0.3 volt-0.4 volt-0.5 volt-0.6 volt-0.7 volt-0.8 volt-0.9 volt-1.0 volt0.1 volt0.2 volt0.3 volt0.4 volt0.5 volt  Fig. 2 – I-T Characteristics of Ga-Si(p) Schottky diode at dif-ferent voltages before correction  The equivalent circuit of a practical Schottky diode generally includes a series and a shunt resistance be-sides a capacitance in parallel to the junction. The pres-ence of series and shunt resistances can affect the meas-ured I-V data as pointed in our earlier paper [3]. There-fore, more realistic I-V characteristics were obtained after corrections made as discussed earlier and the re-sulting I-T characteristics at different biases is shown in Fig. 3. This shows that the observed anomaly is true one in the present case although its observed magnitude is reduced by presence of these parasitic components.  -0.0001-0.00008-0.00006-0.00004-0.0000200.000020.000040.000060.000080.0001294 295 296 297 298 299 300 301 302 303 304 305 306I (A)T (K)-.3V-.6V-.9V Fig. 3 – I-T Characteristics of Ga-Si(p) Schottky diode at different voltages after correction  The C-V-T data obtained on the Schottky contact was plotted (Fig. 4) to show variation of capacitance with temperature at fixed biases. From here it can be seen that there is significant change in the trend of varia-tion in the magnitude of exhibited capacitance values. 02E-104E-106E-108E-101E-091.2E-091.4E-09296 298 300 302 304 306 308 310Capacitance (F)T (K)V=-0.5voltV=-1.0voltV=-1.5volt Fig. 4 – Capacitance vs Temperature of Ga-Si (p) Schottky diode at different voltages   To make it more apparent, the rate of change of capaci-tance values at these different fixed biases were plot-ted. This is shown in Fig. 5. It is seen that a similar kind of anomaly as seen in current voltage characteris-tics around melting point of gallium is also visible in the capacitance voltage characteristics.  05E-121E-111.5E-112E-112.5E-11296 298 300 302 304 306 308 310[dC/dT] (F/K)T (K)V= -V= -1.0 VV= -2.0 V  Fig. 5 – (dC) / (dT) (F / K) vs Temperature of Ga-Si(p) Schott-ky diode at different voltages  I-V-T and C-V-T behaviour of Schottky contacts originate from interfacial dipole layer characteristics and charge transport mechanisms through it [6]. As far as charge transport in the present case is concerned, it is thermionic emission. Such an inference is based on:  the doping density in the semiconductor used (sili-con in the present case) is not high and the tempera-ture at which characteristics are being observed is not very low to warrant tunneling as the dominating charge transport mechanism,   the characteristics energy E00, as calculated in pre-sent case, is not of the order of kT to warrant thermionic field emission as dominant charge transport mechanism. On the contrary E00 is more than ten orders lower than kT as required for identifying ther-mionic emission as dominant charge transport mechanism. Analyzing the observed behaviour on such basis shows that the ideality factor is around 1.1 at all tem-peratures. However, the flat band barrier height and built in potential show a decrease near the melting point of gallium Fig. 6.  PHASE TRANSITION SENSITIVE SCHOTTKY BARRIERS … J. NANO- ELECTRON. PHYS. 5, 02005 (2013)   02005-3 0.780.80.820.840.860.880.90.920.94290 295 300 305 31000.10.20.30.40.50.60.70.80.91290 295 300 305 310Built in potential (eV)Flat Band Barrier Height (eV)Temperature KFlat Band barrier height(eV)  Fig. 6 – Flat band barrier height and built-in volt potential variation with temperature for Ga-Si(p) diode  It has been reported in the literature [7-9] that the Schottky diode behaviour in general have contributions both from the bulk materials used in the contact as well as their interface. Therefore, it can be thought that the observed anomaly around the phase transition of galli-um is driven by changes in the bulk properties of galli-um or its interface with silicon, since the bulk properties of silicon are not expected to show any significant change around this temperature. Moreover, the contact with liquid gallium has been made immediately on the cleaned and etched silicon surface leaving little time for formation of oxide layer of any significant thickness. Melting/solidification of a substance is a phase transition of the first kind. It is seen that in such phase transitions there is a rearrangement of crystal lattice of the substance consisting of changes in the interatomic distances and the angle between lattice planes. As a result the symmetry of the substance changes discon-tinuously. At the same time there is a discontinuous change in the volume and density as well. There is also a change in the internal energy accompanied by evolu-tion or absorption of heat energy, which is known as latent heat of transition and does not appear as an  apparent change in the temperature of the substance. All this occurs over a narrow range of temperature cen-tered on the phase transition temperature. The ther-modynamic conditions of equilibrium for these kinds of discontinuous changes between phases of different symmetry require that such transitions occur at con-stant temperature and pressure. But in processes oc-curring at constant pressure the quantity of heat ab-sorbed by the body is equal to change in its heat func-tion and consequently the entropy also undergoes a change during such phase transitions. Analyzing the effect of this kind of changes in the internal energy of bulk gallium on the saturation current and consequent-ly on the barrier height, it is found that it is negligible as compared to the observed changes. This is also certi-fied by the fact that no anomalous change in the resis-tivity of gallium has been reported around the melting point of gallium [10]. Moreover, it has also been report-ed that structural disturbances set-in very slowly in gallium on melting. It has also been reported [11] from the structure-factor variation study across the melting point of gallium that the number of nearest neighbors and the sphere of first coordination remain almost un-changed over a temperature range of 203 K to 323 K. Therefore, it seems that the observed anomaly origi-nates predominantly from changes at the interface around the melting point of gallium and not from changes in the bulk properties of gallium. It may be noted that in case of solid-solid interface Schottky di-odes, the contribution from interface is usually masked by the contributions from the bulk unless the thickness of metallic over layer coverage is few mono layers only. Exceptions to this have been reported rarely [7, 8]. Interfacial changes near the phase transition tem-perature are likely to give rise to build up or relaxation of bonds between gallium and silicon – while silicon has cubic structure, gallium in the solid state has or-thorhombic structure [12, 13]. Thus, interfacial strain can be expected to give rise to interface states and their additional creation may modify Fermi levels at the in-terface, interfacial band alignment and the barrier height [14-16]. Obviously, the quantum of changes in the barrier height may be expected to depend on both the density of original interface states existing on the semiconductor and the density of interface states aris-ing from interfacial strain. Therefore it can be conclud-ed that the  evolutionary aspects of Schottky diodes e.g. contribution of interfacial strain which are seen only at smaller thicknesses of metallic over layers in case of solid-solid contacts may be seen more clearly in case of solid-liquid contacts.    REFERENCES  1. B.L. Sharma, Metal-Semiconductor Schottky Barrier Junc-tions and Their Applications (Plennum Press: New York and London: 1984). 2. V. Podzorov, M.E. Gershenson, Appl. Phys. Lett. 84, 3301 (2004). 3. B.P. Modi, J.M. Achamma, K.D. Patel, V.M. Pathak, R. Srivastava, Indian J. Pure Appl. Phys. 43, 184 (2005). 4. J.M. Achamma, K.D. Patel, R. Srivastava, Thin Solid Films 518, 2695 (2010). 5. K.D. Patel, Ph.D. thesis, Sardar Patel University, (1997). 6. E.H. Rhoderick, Metal-Semiconductor contacts (Clarendon Press: Oxford, UK: 1978). 7. G. Margaritindo, Rep. Prog. Phys. 62, 765 (1999). 8. U. Rau, H.H. Guttler, J.H. Werner, MRS Proc. 260, 245 (1992). 9. P. Perfetti, Surf. Rev. Lett. 2, 643 (1995). 10. M. Pokorny, H.U. Astrom, J. Phys. F: Met. Phys. 6, 559 (1976). 11. M.P. Bharat, Ph D thesis, Sardar Patel University, (2003). 12. W.F. McClune, Powder Diffraction file JCP DS(1983) 13. J. Wolny, S. Niziol, W. Luznu, L. Pytlik, J. Soltys, R. Kokoszka, Solid State Commun. 58, 573 (1986). 14. Mustafa Okutan, Engin Basaran, Faherttin Yaku-phanoglu, Appl. Surf. Sci. 252, 1966 (2005).  15. R.K. Mamoadov, M.A. Yeganesh, Microelectron. Reliab. 52, 418 (2012). 16. Ashish Kumar, Seema Vinayak, R. Singh, J. Nano-  Electron. Phys. 3 No1, 671 (2011).  

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Phase Transition Sensitive Schottky Barriers In Ga-Si(P) Contacts

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