In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys

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ScienceDirect Materials Today: Proceedings 18 (2018) 1918–1926

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ICSMD-2017

Analysis of thermal annealing effects of Au-Cu/n-GaAs/In and Ag-Cu/n- GaAs/In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys İ. Kanmaz, A. Taşer, S. Küp, B. Güzeldir* and M. Sağlam* Department of Physics, Faculty of Sciences, Atatürk University, 25240 Erzurum, Turkey

Abstract This study focused on the electrical characteristics of Au-Cu/n-GaAs/In and Ag-Cu/n-GaAs/In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys and increased annealing temperature. Firstly, the Au-Cu and Ag-Cu alloys ratio (25%-75%, 50%50%, 75%-25%) characterized by energy dispersive X-ray analysis (EDAX) spectroscopy. The EDAX spectra showed that the expected different ratios metal percent exist in the alloys, approximately. Secondly, the current- voltage (I-V) characteristics of the Au-Cu/n-GaAs/In and Ag-Cu/n- GaAs/In Schottky diodes with different ratios were researched at room temperature. Finally, these diodes at different rates were annealed for 5 minutes at 100, 200 and 300℃ at nitrogen atmosphere and after every annealing process I-V measurements were repeated at room temperature, respectively. The characteristic parameters such as barrier height, ideality factor, series resistance and straighening rates of these diodes were calculated from the forward bias I-V characteristics as a function of annealing temperature with different methods. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of INTERNATIONAL CONGRESS ON SEMICONDUCTOR MATERIALS AND DEVICES. Keywords: Au-Cu and Ag-Cu alloys; EDAX; Schottky diodes; Thermal annealing

* Corresponding author. Tel.: +90 442 2314178; fax: +90 442 2360948. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of INTERNATIONAL CONGRESS ON SEMICONDUCTOR MATERIALS AND DEVICES.

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1. Intoruction Thermal stability and reliability in the characteristics of Schottky barrier diodes (SBDs), which have long been a matter of curiosity, are of practical importance in device technology [1-8]. The performance of the SBDs is largely determined by the quality of interface between the Schottky metal and the semiconductor surface being deposited. Moreover, the reliability of SBDs, the interdiffusion and interaction between these materials is of considerable relevance. Such contact is usually unstable due to the tendency of interdiffusion and compound formation at the interface in device preparation and performance [9, 10]. Recently, various researches have been done on various metal-semiconductor systems due to the practical importance of these systems in forming Schottky contacts in semiconductors [2-6]. Examination of the products of metal / semiconductor reactions has shown that the films of the intermetallic compounds of the semiconductor substrate (containing two or more metals) may be more stable than the only stable metal layers in low temperature annealing [11]. Alloys are made by mixing the metals with carefully measured amounts and combining them with one or more other elements by melting. They are combinations of metals used in a wide variety of applications, may reduce the overall cost of the material by protecting important properties. The electrical and thermal conductivity of alloys is usually lower than that of the pure metals. The physical properties of an alloy may not differ greatly from those of its base element, but some of the properties may be substantially different from those of the constituent materials. This is sometimes a result of the sizes of the atoms in the alloy, because larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation [12-14]. In our study, we investigated thermal annealing effects of Au-Cu/n-GaAs/In and Ag-Cu/n- GaAs/In Schottky diodes with Au-Cu and Ag-Cu alloys which were previously prepared at laboratory at different ratios by means of the I-V measurements in dark at room temperature. 2. Experimental In this study, n-GaAs wafer with [100] orientation 450 μm thickness and 2,5x1017 cm-3 with a doping density was used. n-GaAs wafer was sequentially cleaned with trichloroethylene (CHClCCl2), acetone (CH3COCH3) and methyl alcohol (CH3OH), etched in a sequence of sulfuric acid (H2SO4) and hydrogenperoxide (H2O2) and finally deionized water of resistivity of 18MΩ cm. During to each cleaning step, the wafer was rinsed thoroughly in deionized water. Ohmic contact was performed by evaporating In metal on the mat surface of crystal. And to other surface, Au-Cu/n-GaAs/In and Ag-Cu/n-GaAs/In Schottky diodes were obtained by evaporating of Au-Cu and AgCu alloys which were previously prepared at laboratory at different ratios at 10-5 torr pressure. The Au-Cu and Ag-Cu alloys with different ratios on n-GaAs substrate were characterized, ZEISS SUPRA 50VP scanning electron microscope with an attached energy dispersive x-ray analysis (EDAX) analyser to qualitatively measure the sample stoichiometry. I-V measurements of the diodes were performed at room temperature in dark, using a HP4140B picoampermeter. Moreover, in order to observe the effect of the thermal annealing, the Au-Cu/nGaAs/In and Ag-Cu/n-GaAs/In Schottky diodes were annealed at temperatures 100, 200 and 300◦C for 5min in nitrogen atmosphere, respectively. 3. Results and discussion The EDAX measurement, which is one of the important applications of scanning electron microscope (SEM), is to get information about material composition. This micro-analysis mode of the SEM responds to the observation of x-rays emitted by the surface of the sample under electron radiation. These x-rays can be collected and analyzed to give information about the elemental compounds present in the sample. The result of the EDAX measurement for Au-Cu and Ag-Cu alloys which were prepared with different ratios at 10-5 torr pressure are showed in Fig.1 and Fig. 2. The 25% Au-75% Cu sample was named (a), 50% Au-50% Cu sample was named (b), 75% Au-25% Cu sample was named (c) and 25%Ag-75%Cu sample was named (d), 50% Ag-50% Cu sample was named (e), 75% Ag -25% Cu sample was named (f). The metals with the different ratios analysis was carried out Au-Cu; the average atomic percentage was found to be 25% Au-75% Cu = 11.02 : 60.95 , 50% Au-50% Cu = 24.40 : 22.75, 75% Au-25%Cu =

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35.17 : 22.10 and the Ag-Cu; the average atomic percentage was found to be 25%Ag-75%Cu = 13.28 : 23.56 , 50%Ag-50%Cu = 0.45 : 0.46, 75%Ag-25%Cu = 27.87 : 1.59. The typical EDAX spectra shown in Fig. 1, Fig. 2 and the average atomic percentages indicate that expected different ratios metals have been detected in the Au-Cu and Ag-Cu alloys, approximately. Also, small percentage of Na, Mg, C and O elements is present in the alloys. It is thought that these elements may be probably resulted some of the experimental systems.

Fig. 1 The EDAX images of Au-Cu alloys with different ratios.

Fig. 2 The EDAX images of Ag-Cu alloys with different ratios.

Depending on the thermionic emission, the current through the uniform metal-semiconductor interface can be expressed as [9]:

 qV    qV   1  exp    nkT    kT 

I  I 0 exp

(1)

where I0 is the saturation current given by  2  qap  I o  AA T exp   kT   

(2)

q is the electron charge, V is the forward-bias voltage, A is the effective diode area, k is the Boltzmann constant, T is the absolute temperature, A* is the effective Richardson constant of 8.16 Acm-2K-2 for n-type GaAs, Φap is the zero bias apparent barrier height and n is the ideality factor. From Eq. 2, ideality factor n can be written as n

 dV    kT  d ln I  q

(3)

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The curves in Fig. 3 and Fig. 4 show the experimental semilog forward and reverse bias I-V characteristics of the Au-Cu/n-GaAs/In, Ag-Cu/n-GaAs/In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys as a function of annealing temperature. It is observed that the linear portions of the forward bias lnI vs. V plots indicate that the current at the low voltage region varies exponentially with the voltage. The values of Φb and n after each annealing step were determined from the intercept and slope of the forward-bias ln I versus V plots using Eqs. (2) and (3), respectively and are given in Table 1 and Table 2. Except from Figure 3a, it has been shown that the characteristic parameters of these diodes exhibit a stable structure, which does not significantly change during the heat annealing process up to 3000C. The Au-Cu/n-GaAs/In, Ag-Cu/n-GaAs/In Schottky contacts have given further improved Schottky characteristics as a result of sufficiently the annealing temperatures. The curves in Fig. 3a rectifying property of the diode decreases with the thermal annealing. Values of n slightly larger than unity confirm that there exists an interfacial native oxide layer between the Au-Cu, Ag-Cu and GaAs interface. The interface states and interfacial-oxide layer at the metal-semiconductor rectifying contacts play an important role in the determination of the Schottky barrier height and other characteristic parameters of the devices. The surface states can be viewed as electronic states generated by unsaturated dangling bonds of the surface atoms. In the laboratory environment, crystal surfaces are usually covered with layers of native oxides and organic contaminants. It is now well accepted that reactive metals such as calcium and aluminum interact chemically with the semiconductor and lead to new chemical species, which in turn deeply affect its electronic structure and, hence, the electronic process taking place at the interface. The observed interface efects are general phenomena on compound semiconductor surfaces and metals which react with native oxides may be preferred in actual devices [15]. 1E-002

Current (A)

Current (A)

1E-005 1E-006 1E-007 1E-008

As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E-010 1E-011 -0.8 -0.6 -0.4 -0.2

0

0.2

Voltage (V)

0.4

0.6

0.8

1E-003

1E-004

1E-004

1E-005 1E-006 1E-007

As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E-010

1E-006 1E-007

%75Au-%25Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E-009 1E-010

1E-011 -0.8 -0.6 -0.4 -0.2

1E-005

1E-008

%50Au-%50Cu

1E-009

1 -1

1E-002

1E-003

1E-008

%25Au-%75Cu 1E-009

(c)

1E-002

1E-004

-1

1E-001

1E-001

(b)

1E-003

Current (A)

(a)

1E-011 0

0.2

Voltage (V)

0.4

0.6

0.8

-1 1

-0.8 -0.6 -0.4 -0.2

0

0.2

Voltage (V)

0.4

0.6

0.8

1

Fig. 3 The semi-log forward and reverse bias current-voltage characteristics of Au-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios (a) %25Au-%75Cu, (b) %50Au-%50Cu and %75Au-%25Cu alloys.

1E-001

1E-002

1E-001

(a)

(b)

1E-002

(c)

1E-003

1E-002 1E-003

1E-003

1E-004

1E-004

1E-006 1E-007 1E-008

%25Ag-%75Cu As-deposited 100 oC Anealed 200 oC Anealed 300 oC Anealed

1E-010 1E-011

1E-007

1E-010 1E-011

0

0.2

Voltage (V)

0.4

0.6

0.8

1-1

-0.8 -0.6 -0.4 -0.2

0

0.2

Voltage (V)

0.4

0.6

0.8

1E-005 1E-006 1E-007 1E-008 1E-009

%50Ag-%50Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E-009

1E-012 -0.8 -0.6 -0.4 -0.2

1E-006

1E-008

1E-009

-1

Current (A)

1E-005

1E-005

Current (A)

Current (A)

1E-004

%75Ag-%25Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E-010 1E-011 1E-012 -1 1

-0.8 -0.6 -0.4 -0.2

0

0.2

Voltage (V)

0.4

0.6

0.8

1

Fig. 4 The semi-log forward and reverse bias current-voltage characteristics of Ag-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios (a)%25Ag-%75Cu, (b) %50Ag-%50Cu and (c) %75Ag-%25Cu alloys.

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At annealing temperatures, assuming the transport mechanism is due to thermionic emission and attributing the deviation from linearity to series resistance, the Φb and n value of these curves was determined applying the analysis of Cheung and Norde methods. The following function has been defined in the modified Norde’s method [16]:



FV 

V





 I V     AA*T 2 

kT

ln

q

(4)

where  is an arbitrary integer (dimensionless) greater than n. I(V) is current obtained from the I-V curve. From the value of F(V0,I0) and the corresponding current I, at the minimum, the barrier height and the series resistance can be obtained:

 

b  F Vo 

Rs 



kT   n

Vo





kT

(5)

q



(6)

qI

Fig. 5 and Fig. 6 show the F(V)-V plots of the Au-Cu/n-GaAs/In, Ag-Cu/n-GaAs/In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys as a function of annealing temperature. The values of the barrier height and series resistance have been obtained from Norde’s method by using Eqs. 5 and 6 and given in Table 1, Table 2.

0.94

1.15

(a)

1.10

0.94

(b)

0.92 0.90

0.90

1.00

0.95

%25Au-%75Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

0.90

0.85

0.86 0.84 0.82

%50Au-%50Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

0.80 0.78 0.76 0.74

0.80 0.2

0.4

0.6

0.8

V (Voltage)

1

1.2

F(V) (Voltage)

0.88

F(V) (Voltage)

F(V) (Voltage)

1.05

(c)

0.92

0.88 0.86 0.84 0.82

%75Au-%25Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

0.80 0.78 0.76

0.2

0.4

0.6

0.8

V (Voltage)

1

1.2

0.4

0.6

0.8

V (Voltage)

1

1.2

Fig. 5 Experimental F(V)-V curves of Au-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios (a) %25Au-%75Cu, (b) %50Au-%50Cu and %75Au-%25Cu alloys.

The Cheung’s functions can be written as follow [17]; dV

 

d ln I



nkT q

 IRs

(7)

İ. Kanmaz et al. / Materials Today: Proceedings 18 (2018) 1918–1926 0.94

(a)

1.00

1.04

0.92

1923

(b)

(c)

0.98

1.00 0.96

0.88

0.86

%25Ag-%75Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

0.84

0.82

0.80 0.5

0.6

0.7

0.8

V (Voltage)

0.9

F(V) (Voltage)

0.96

F(V) (Voltage)

F(V) (Voltage)

0.90

0.92

0.88

%50Ag-%50Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

0.84

0.80

0.76 1

0.2

0.4

0.6

V (Voltage)

0.8

1

0.94 0.92 0.90 0.88

%75Ag-%25Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

0.86 0.84 0.82 0.4

0.6

0.8

V (Voltage)

1

1.2

Fig. 6 Experimental F(V)-V curves of Ag-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios (a)%25Ag-%75Cu, (b) %50Ag-%50Cu and (c) %75Ag-%25Cu alloys.

 nkT   I   ln  2   q   AA T 

H(I) = V- 

(8)

H ( I )  nb  IRs

(9)

where Φb is the barrier height obtained from data of downward curvature region in the forward bias I-V characteristics. Equation (7) should give a straight line for the data of downward curvature region in the forward bias I-V characteristics. The slope of the linear part of the dV/d(lnI) versus will give Rs and its y-axis intercept will give nq/kT. Using the n value determined from equation (7) and the data of downward curvature region in the forward bias I-V characteristics in equation (8), a plot of H(I) versus I according to equation (8) will also give a straight line with y-axis intercept equal to nΦb. These values are shown in Table 1 and Table 2 for Au-Cu/n-GaAs/In, Ag-Cu/nGaAs/In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys as a function of annealing temperature. It can clearly be seen that there is a relatively a high difference between the values of the ideality factor obtained from the downward curvature region of forward bias I-V plots and from the linear regions of the same characteristics. The reason for this difference can be attributed to the existence of effects such as the series resistance and the bias dependence of the Schottky barrier height, according to the voltage drop across the interfacial layer and charge of the interface states with bias in this concave region of the I-V plot [18]. The series resistances increased with increasing annealing temperature. These originate from the increase of indifused Au-Cu and Ag- Cu alloys atoms leading to the formation of a highly resistive layer at the Au-Cu/n-GaAs and Ag-Cu/n-GaAs interfaces at each anneal step or from the edge-related current. An Rs value higher than the predicted one can be explained in terms of the bias dependence of the barrier height which is caused by a highly resistive interfacial layer formed at each anneal step. As is known, the barrier height becomes bias-dependent due to the potential change across the interfacial layer as a result of the applied voltage. Therefore the concavity of the current voltage curve especially at high currents or voltages increases owing to the fact that the bias- dependent barrier height increases with increasing forward bias voltage [19-21]. Also, it can be said that, especially, the values of series resistance obtained from both methods are slightly different from each other. In most cases, the parameters obtained from Cheung functions and Norde’s functions are not in agreement with each other. Because, Cheung functions are only applied to the nonlinear region (high voltage region) of the semi-log forward bias I-V characteristics whereas, Norde’s functions are applied to the full forward bias I-V characteristics of the junctions. According to Fig. 3 and Fig. 4, the variation of the rectifying ratio with respect to applied voltage can be given easily for Au-Cu/n-GaAs/In, Ag-Cu/n-GaAs/In Schottky diodes with increasing annealing temperature. The plot can be seen in Fig.7 and Fig. 8. In these figures, the rectifying ratio has slightly decreased with respect to the asdeposited sample. In other words, the rectifying ratio of the Au-Cu/n-GaAs/In, Ag-Cu/n-GaAs/In Schottky diodes remains almost constant with thermal treatment.

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1E+007

1E+005

1E+006

Rectifying Ratio

1E+006

1E+004 1E+003

%25Au-%75Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E+002 1E+001 1E+000

(b)

1E+008

1E+007 1E+006

1E+005 1E+004

%50Au-%50Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E+003 1E+002 1E+001

0.1

0.2

0.3

0.4

0.5

0.6

0.7

V (Voltage)

0.8

0.9

1

1E+004

%75Au-%25Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E+003

1E+001 1E+000 1E-001

0.1

1.1

1E+005

1E+002

1E+000

1E-001

(c)

1E+008

Rectifying Ratio

(a)

1E+007

Rectifying Ratio

1E+009

1E+009

1E+008

0.2

0.3

0.4

0.5

0.6

0.7

V (Voltage)

0.8

0.9

1

0.1

1.1

0.2

0.3

0.4

0.5

0.6

0.7

V (Voltage)

0.8

0.9

1

1.1

Fig. 7 The rectifying ratio versus applied voltages for Au-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios (a) %25Au-%75Cu, (b) %50Au-%50Cu and %75Au-%25Cu alloys.

1E+009

1E+008

(a)

1E+008

1E+007

1E+007

(c)

1E+008 1E+007

1E+006

1E+005 1E+004 1E+003

%25Ag-%75Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E+002 1E+001 1E+000 1E-001

0.2

0.3

0.4

0.5

0.6

0.7

V (Voltage)

0.8

0.9

1

1E+005 1E+004

%50Ag-%50Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E+003 1E+002 1E+001

1E-002 0.1

1E+006

1.1

Rectifying Ratio

Rectifying Ratio

1E+006

Rectifying Ratio

1E+009

(b)

1E+005 1E+004 1E+003

%75Ag-%25Cu As-deposited 100 oC Annealed 200 oC Annealed 300 oC Annealed

1E+002 1E+001 1E+000 1E-001

1E+000

1E-002 0.1

0.2

0.3

0.4

0.5

0.6

0.7

V (Voltage)

0.8

0.9

1

1.1

0.1

0.2

0.3

0.4

0.5

0.6

0.7

V (Voltage)

0.8

0.9

1

1.1

Fig. 8 The rectifying ratio versus applied voltages for Ag-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios (a)%25Ag-%75Cu, (b) %50Ag-%50Cu and (c) %75Ag-%25Cu alloys.

Table 1.The experimentally obtained from different methods ideality factor n, barrier height Φb, saturation current I0 and series resistance Rs values of Au-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios Au-Cu alloys. Au-Cu/nAnn. Temp. (0C) GaAs/In 25% Au 75% Cu

50% Au 50% Cu

75% Au 25% Cu

As. Dept. 100 200 300 As. Dept. 100 200 300 As. Dept. 100 200 300

I-V Method n 1,1 1,18 1,26 1,49 1,1 1,11 1,18 1,24 1,08 1,07 1,07 1,04

Фb (eV) 0,86 0,87 0,87 0,83 0,81 0,82 0,85 0,85 0,85 0,93 0,86 0,83

I0 (A) 2,40E-11 1,58E-11 1,38E-11 5,84E-11 1,57E-10 1,05E-10 3,18E-11 3,47E-11 2,59E-11 1,21E-12 2,35E-12 7,93E-11

Cheung Method n 1,35 1,43 1,43 1,74 1,58 1,66 1,7 1,82 1,28 1,31 1,39 1,7

Rs 122,93 790,4 6599,52 44148,49 5,87 7,02 9,87 7,4 7,37 4,94 5,81 10,36

Фb (eV) 0,83 0,86 0,84 0,81 0,68 0,69 0,72 0,71 0,89 0,86 0,79 0,68

Norde Method Rs 124,3 808,11 6673,1 44710,7 5,95 7,08 9,96 7,34 7,47 5,04 5,87 10,49

Фb (eV) 0,85 0,87 0,86 0,82 0,81 0,82 0,84 0,83 0,86 0,94 0,86 0,83

Rs 127,25 520,04 3997,39 32423,29 7,19 10,76 14,34 19,76 5,54 6,68 7,97 13,28

İ. Kanmaz et al. / Materials Today: Proceedings 18 (2018) 1918–1926

1925

Table 2. The experimentally obtained from different methods ideality factor n, barrier height Φb, saturation current I0 and series resistance Rs values of Ag-Cu/n-GaAs/In Schottky diodes as a function of annealing temperature with different ratios Ag-Cu alloys. AgCu/nGaAs/In

Ann. Temp. (0C) n

Фb (eV)

I0 (A)

n

Rs

Фb (eV)

Rs

Фb (eV)

Rs

25% Ag 75% Cu

As. Dept. 100 200 300

1,13 1,12 1,09 1,09

0,86 0,87 0,86 0,85

1,89E-11 1,20E-11 1,83E-11 2,96E-11

1,66 1,31 1,66 1,82

5,05 3,63 4,65 5,2

0,78 0,89 0,76 0,72

5,07 3,7 4,81 5,31

0,87 0,86 0,86 0,85

4,15 5,8 6,63 10,8

50% Ag 50% Cu

As. Dept. 100 200 300

1,07 1,09 1,21 1,25

0,77 0,8 0,83 0,85

7,31E-10 1,93E-10 7,51E-11 2,73E-11

1,17 1,21 1,07 1,06

115 111,03 487,48 513,16

0,75 0,78 0,89 0,95

115,29 110,86 499,88 526,2

0,77 0,8 0,82 0,84

134,49 144,46 347,64 415,55

As. Dept.

1,12

0,85

3,37E-11

1,34

7,89

0,85

8,02

0,84

10,03

100

1,16

0,84

4,75E-11

1,39

16,56

0,84

16,98

0,83

22,16

200

1,12

0,89

7,09E-12

1,74

15,03

0,76

15,86

0,84

32,61

300

1,12

0,89

7,79E-12

2,13

65,22

0,7

57,38

0,84

65,55

75% Ag 25% Cu

I-V Method

Cheung Method

Norde Method

It is observed that the change of barrier height and ideality factor in the diodes are less change depending on the annealing temperature. Since it is one of the main objectives to obtain a stable diode characteristics depending on the annealing temperature, these diodes are more preferable than the other metal/semiconductor diodes. In addition, the barrier of the samples are inhomogeneous and the I-V characteristics can also be explained in terms of spatial inhomogeneity of the Schottky barrier height. The Schottky barrier height is likely to be a function of the interface atomic structure and the atomic inhomogeneities at the MS interface are caused by grain boundaries, multiple phases, facets, defects, a mixture of different phases, etc. In such cases, the current across the MS contact may be significantly affected by the presence of Schottky barrier inhomogeneity. The stability and reproducibility of contact properties and the formation of a high quality Schottky barrier diode are essential prerequisites for improvement of device performance. Choosing semiconductor and fabrication methods should be good agreement for the development of device characteristics. The alloys with different ratios are promising technique that allow good electrical properties. The reactive contact metal results in a different metallic-like phase at the MS interface by reacting with the semiconductor during heat treatment and can cause a low or high Schottky barrier height by means of Fermi-level pinning. That is, a stable contact can be obtained by utilizing intermetallic compounds formed viasolid state reactions between the metal and the GaAs substrate. A reacted contact is thermodynamically stable and has a much better quality than previous works [22-25]. In addition, investigations of the product of metal/GaAs reactions have shown that of intermetallic compounds on the GaAs substrate maybe more stable compared to single metal layers which are stable [26]. Therefore, we have used with different ratios Au-Ag and Au-Cu alloys as contact material and have investigated the effects of different ratios and annealing temperature on the current-voltage characteristics of Schottky barrier diodes and therefore on the formation of the Schottky barrier height. 4. Conclusion In this study, we prepared Au-Cu/n-GaAs/In and Ag-Cu/n-GaAs/In Schottky diodes with different ratios Au-Cu and Ag-Cu alloys and investigated the electrical stability of this structure by the I-V measurements. It has been shown that the characteristic parameters of these diodes are not remarkably changed in the thermal annealing up to 3000C and the Au-Cu/n-GaAs/In, Ag-Cu/n-GaAs/In Schottky contacts have given further improved Schottky characteristics as a result of sufficiently the annealing temperatures. The Schottky barrier formation is determined by a complicated mixture of phases at the interface resulting from chemical reactions between the metal contact and GaAs. Therefore it has been found that the Au-Cu/n-GaAs and Ag-Cu/n-GaAs barrier heights remain reasonably stable up to 3000C and thermally becomes more stable.

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