IPASJ International Journal of Electrical Engineering (IIJEE)
Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
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ISSN 2321-600X
A Publisher for Research Motivation........
Volume 2, Issue 8, August 2014
The Impact of Cu Doping Ratio on Electrical
Properties for Thin ZnO Films Prepared by
PLD
Kh. M. Rashid1 and M.F.A.Alias2
1
2
Department of Physics, College of Science, University of Baghdad, , Baghdad, Iraq
Department of Physics, College of Science, University of Baghdad P.O.Box 47162 Jadiriyah, Baghdad, Iraq
ABSTRACT
In present work, thin doped ZnO films are prepared by pulse laser deposition (PLD) technique at different Cu doping ratio ( 0,
2, 4, 6, 8 and10) wt % on glass substrates .The DC electrical properties of prepared specimens have been investigated as a
function of various Cu doping ratio. These measurements show that the DC conductivity at room temperature increases with
increasing Cu doping ratio from 0 to 10 wt%. The films have two activation energy and they decreases with increasing Cu
concentration. All the prepared ZnO films doped with Cu have n- type. The carrier concentration of films increases, while the
mobility decreases with increasing Cu doping ratio.
Keywords: ZnO thin film, pulse laser deposition, electrical properties, Cu concentration.
1. INTRODUCTION
Zinc oxide (ZnO) is one of the earliest oxides which have attracted a great deal of attention for application as sensors
because of its sensitivity to different absorbed gases, high chemical stability, nontoxicity and low cost [1].Recent
improvements in the quality and control of conductivity in bulk and epitaxial ZnO have increased interest in the use of
this material for short wavelength light emitters and transparent electronics [1],[ 2]. Zinc oxide (ZnO) is an important
electronic and photonic material because of its wide-bind semiconductor with a band gap of about to 3.37eV and large
exciton binding energy of 60meV [3]-[5]. Many different techniques such as chemical vapor deposition, organic
chemical vapor deposition (MOCVD), plasma-assisted molecular beam epitaxy (PA-MBE), pulsed laser deposition
(PLD), and spray pyrolysis technique have been used to growth the ZnO [6]-[8]. The present work is to study the effect
of Cu dopant ratio on electrical properties of ZnO thin films fabricated using pulsed laser deposition technique. This
method is much less complicated than the techniques currently used for fabrication.
2. EXPERIMENTAL PROCEDURE
Pure zinc oxide powder and different doping concentrations for Cu with high purity (99.999%) were prepared by
pressing them under 5 Ton to formed a target with 2.5 cm diameter and 0.4 cm thickness. It should be as dense and
homogenous as possible to ensure a good quality of the deposit. ZnO:Cu thin films were prepared on cleaned glass
substrates using pulse laser deposition (PLD) technique(Nd:YAG (HuafeiTongda Technology—DIAMOND-288
pattern EPLS)) which carried out inside a vacuum chamber generally at (10-3Torr). The thickness of prepared films
was about 130 nm which measured by Michelson interferometer. Ohmic contacts for the prepared films are produced by
evaporating Al electrodes of 300 nm thickness on the samples using appropriate masks, by means of thermal
evaporation methods, using Edward coating unit model (606) under high vacuum (10-5m bar) . The films glass
samples are heated in the oven from room temperature up to 523K with step of 283K.Electrical resistance is then
measured directly for all steps with digital electrometer. The activation energy is calculated from measuring the
conductivity as a function of temperature. The temperature read out is by (MANFREDI L7C). The bias voltage was
supplied by (FARNELL E 350) power supply. The current read out is by Kithley-616 Digital Electrometer.
The resistivity (ρ) of the films is calculated by using equation [9]:

R .A
L
.
(1)
where R is the sample resistance, A is the cross section area of the films and L is the distance between the electrodes.
The conductivity (  d .c ) of the films was determined from the relation:
 d .c 
1

Volume 2, Issue 8, August 2014
.
(2)
Page 1
IPASJ International Journal of Electrical Engineering (IIJEE)
A Publisher for Research Motivation........
Volume 2, Issue 8, August 2014
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Email: editoriijee@ipasj.org
ISSN 2321-600X
The activation energies (Ea) could be calculated from the plot of lnσ versus 1000/T using the equation[9]:
 Ea
 d .c   o exp
K BT
(3)
Hall Effect measurement has been done by Van der Pauw (Ecopia HMS-3000) Hall Measurement Systems by a
magnetic field (B=0.550 Tesla) applied perpendicular to the Hall element. The carrier concentration (n) is related to the
Hall coefficient (RH) which is given by
RH 
1
qn
(4)
The Hall mobility (H) can be found from relation between Hall coefficient and conductivity ()[10].

H 
 RH 
nq
(5)
3. RESULTS AND DISCUSSION
Figure (1) shows the variation of Ln (σ) with reciprocal temperature for deposited ZnO films with different Cu doping
ratio (0, 2, 4, 6, 8 and 10) wt%. This figure shows that all films have two activation energies and these activation
energies decrease with increasing doping ratio ,i.e, it decreases about four times for Ea1 ( 0.222 - 0.057 ) eV and nearly
five times for Ea2 (0.593 - 0.127) eV when the Cu ratio vary from 0 to 10%. This result may due to decrease energy gap
with the increase of doping ratio. All these values have been listed in Table (1). These results are in agreement with
Yoon et al.[11] and Bouhssira et al.[12].
Figure 1 Variation of Ln (σ) with reciprocal temperature for deposited thin ZnO films at different Cu doping ratio.
Figure 2 Variation of DC activation energies with Cu doping ratio for thin ZnO films.
Volume 2, Issue 8, August 2014
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IPASJ International Journal of Electrical Engineering (IIJEE)
Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
Email: editoriijee@ipasj.org
ISSN 2321-600X
A Publisher for Research Motivation........
Volume 2, Issue 8, August 2014
Figure 3 Variation of DC conductivity at room temperature with Cu doping ratio for thin ZnO films.
Table 1 DC activation energies, their ranges and conductivity at room temperature for thin ZnO films at different Cu
doping ratio
Cu%
σRT (Ω.cm) -1
Ea1 (eV)
0
2
4
6
8
10
6.55*10-7
5.04*10-6
5.72*10-5
1.20*10-4
2.98*10-4
1.20*10-3
0.222
0.114
0.094
0.083
0.035
0.057
Range of
Temp.(K)
293-373
293-373
293-373
293-373
293-373
293-373
Ea2 (eV)
Range of
Temp. (K)
373-473
373-473
373-473
373-473
373-473
373-473
0.593
0.519
0.254
0.230
0.172
0.127
n*1015 (cm-3)
The Hall measurements indicates that the pure ZnO and ZnO:Cu films were n-type, this goes in agreement with the
previous work [13]. (Hall voltage values decrease when the current increases). Figures (4 and 5) show the variation of n
carrier concentration and mobility (μH) with different Cu dopant ratio. The values of RH , n and μH at different doping
ratio of Cu are given in Table (2). It is seen that n value increases with increasing Cu doping ratio, while the Hall
mobility (μH) of the ZnO:Cu films decreases with increasing doping ratio. This behavior is expected as a result of the
substitution doping of Cu 2+ site creating one extra free carrier in the process. As the doping level is increased, more
dopant atoms occupy lattice sites of zinc atoms resulting in more charge carriers. Thus, the conductivity increases with
increasing dopant ratio [14]. The ZnO film generally grows as an n-type semiconductor, due to the presence of native
defects in the form of zinc interstitials, oxygen vacancies, or both. A decrease in μH with dopant ratio may be due to
impurity scattering from the substitution donors and scattering from the interstitials and decreasing grain size which
leads to increase grain boundaries [15].
0
5
doping% 10
15
Figure 4 Variation of carrier concentration (n) with different dopant ratio for thin ZnO films
.
Volume 2, Issue 8, August 2014
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IPASJ International Journal of Electrical Engineering (IIJEE)
Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
Email: editoriijee@ipasj.org
ISSN 2321-600X
A Publisher for Research Motivation........
Volume 2, Issue 8, August 2014
Figure 5 Variation of mobility (μ) with different dopant ratio for thin ZnO films.
Table 2 Hall measurements of ZnO thin films prepared at different Cu dopant ratio
Cu %
RH (cm3/c)
nH (cm-3)
μH (cm2/V.sec)
type
0
-1.20*108
5.00 *1010
78.6
n
2
-1.20*10
7
5.20*1011
60.5
n
-8.50*10
5
7.35*10
12
48.6
n
6
-2.60*10
5
2.40*10
13
31.2
n
8
-5.40*104
1.16*1014
16.1
n
14
09.0
n
4
10
-75*10
3
8.00*10
4. CONCLUSIONS
Electrical properties of pure and Cu doped thin ZnO films deposited by pulse laser deposition technique have been
studied as a function of different Cu dopant ratio. The outcome of this investigation can be summarized as follows:
 Pure and doped ZnO films have two activation energies and with increasing doping ration these activation energies
decrease while the conductivity decreases.
 Hall Effect measurements show that all films have n- type charge carriers and its concentration increases whereas
the mobility decreases with increasing doping ratio.
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IPASJ International Journal of Electrical Engineering (IIJEE)
A Publisher for Research Motivation........
Volume 2, Issue 8, August 2014
Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
Email: editoriijee@ipasj.org
ISSN 2321-600X
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