p-Si structure with GO doped NiO interlayer in dark and under light illumination

Journal of Alloys and Compounds 718 (2017) 75e84

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Electrical and photovoltaic properties of Ag/p-Si structure with GO doped NiO interlayer in dark and under light illumination a € Halil Ozerli , Ahmet Bekereci a, Abdulmecit Türüt b, S¸ükrü Karatas¸ a, c, * a

Kahramanmaras Sutcu Imam University, Department of Materials Science and Engineering, Kahramanmaras¸, 46100, Turkey Istanbul Medeniyet University, Faculty of Sciences, Engineering Physics Department, TR-34730, Istanbul, Turkey c Kahramanmaras Sutcu Imam University, Faculty of Sciences and Arts, Department of Physics, Kahramanmaras, 46100, Turkey b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 March 2017 Received in revised form 9 May 2017 Accepted 11 May 2017 Available online 13 May 2017

In our work, graphene oxide (GO) doped nickel oxide (NiO) nanocomposite was used an interfacial layer to investigate electrical and photovoltaic properties of the Ag/p-Si metal semiconductor structures. GO doped NiO nanocomposite films were prepared by Hummers method. This nanocomposite films were characterized by EDX and SEM analyses. The electrical and photovoltaic characteristics of the Ag/GOdoped NiO/p-Si heterojunction were investigated using current-voltage (I-V) and capacitance-voltage (C-V) measurements under dark and 30 mW/cm2 light illuminations conditions at room temperature. The values of ideality factor, reverse saturation current, and barrier height were obtained as 4.52, 1.66
1010 A, and 0.903 eV; 4.38, 3.12
1010 A and 0.887 eV in dark and under light illumination, respectively. At the same time, the interface state densities as a function of energy distributions was extracted from the forward-bias IeV measurements. Experimental investigations show an increase in a reverse current in photodiodes with increasing the illumination intensity. © 2017 Elsevier B.V. All rights reserved.

Keywords: Ag/Go doped NiO/p-Si structure Interlayer Main electrical parameters Interface states

1. Introduction In the recent years, researchers have identified graphene-based semiconductor devices as a possible future alternative to metalsemiconductor technology. Thus, graphene nanocomposite materials are considered one of the most promising candidates for future semiconductor industry applications because of their successful applications in optical and electronic devices [1e4]. Because, graphene is a zero-gap semiconductor having a high intrinsic carrier mobility [1,2]. This situation makes it possible to control the conduction of graphene with the use of a gate [5]. There have been growing interest in the field of graphene oxide nanocomposite materials due to excellent in-plane mechanical, structural, thermal and electrical properties of graphite [1e4]. Graphene oxides are important materials and can be used instead of pure graphene for nanocomposite formation and graphene can be synthesized by different methods [6e22]. There are different methods developed to produce GO doped NiO nanocomposite films in the literature [7e22]. In this study, GO doped NiO nanocomposite films were

* Corresponding author. Kahramanmaras Sutcu Imam University, Faculty of Sciences and Arts, Department of Physics, Kahramanmaras, 46100, Turkey. E-mail address: [email protected] (S¸. Karatas¸). http://dx.doi.org/10.1016/j.jallcom.2017.05.121 0925-8388/© 2017 Elsevier B.V. All rights reserved.

prepared by Hummer's method [17]. Because, graphene oxide can be easily synthesized by Hummer's method. Also, Hummer's method has various advantages such as simplicity, homogeneity, layers of many compositions on various substrates and low production costs. Metal oxide semiconductors (MOS) structures are future availability for electronic and optoelectronic applications. There are some studies about Schottky diodes based on GO-doped NiO. One of this structures is nickel oxide, NiO with a wide band gap of 3.6e4.0 eV [23]. Stengl et al. [24], show that doping TiO2 with GO reduces the nanocomposite optical band gap to below 2.50 eV. Thus NiO is interesting material due to its low material cost, optical properties, promising ion storage. Zhao et al. [25] fabricated the two-dimensional graphene/NiO composite material via selfassembly method. Hendi et al. [26] were investigated photoresponse properties of Al/p-Si/GO:TiO2/Au diodes using transient photocurrent and conductance spectroscopy techniques. Najla [27] was investigated electrical and photoconductivity properties of Al/ graphene oxide doped NiO nanocomposite/p-Si/Al photodiodes with various graphene oxide contents. Çiçek et al. [28,29] were produced with and without interlayer to evaluate synthesis and characterization of pure and graphene (Gr)-doped organic/polymer nanocomposites on the electrical parameters of Au/n-GaAs devices.

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Kaya et al. [30] were investigated electrical characteristics of the Au/n-Si (MS)-type SBD with and without a 2% GC-doped Ca3Co4Ga0.001Ox interfacial. Zhua et al. [31] have reported the effect of graphene oxide on the nanomechanical reinforcement, nanoscratch resistance, and thermal stability of PVA, which were studied from nanoscale to macroscale for the first time, and they demonstrated that the incorporation of 0.5 wt% GO in PVA gives the highest improvement in nano-mechanical properties. Chengpeng et al. [32] have presented PVA and PVA/graphene composites. Shao et al. [33] has been prepared graphite oxide was prepared from graphite using Hummers method [17]. Thus, due to the technological importance of electronic circuit components which are among the most simple of the graphene-Si contacts [5,34], a full understanding of the nature of their electrical and photovoltaic properties are of great interest. In the previous study [34], we were investigated illumination impact on electrical properties of Ag/nGO-PVA/p-Si heterojunction. As different previous study [34], In this study, our purpose is to experimentally investigate the relationship among the electrical, photovoltaic and interface state densities of the Ag/GO-doped NiO/ p-Si heterojunction using current-voltage (I-V) and capacitancevoltage (C-V) measurements under dark and 30 mW/cm2 light illuminations conditions at room temperature. Therefore, this study can be divided into three categories: first, our aim is to investigate the SEM image of GO-NiO structure by means of scanning electron microscope (SEM-Zeiss EVO 10LS) with energy dispersive X-ray spectrometry (EDX). The second goal is to investigate the electrical and photovoltaic properties of the Ag/GO-NiO/p-Si heterojunction by means of I-V and C-V measurements under dark and illuminated conditions. The third goal is to investigate as a function of energy density distribution profiles of the interface state densities (NSS) obtained from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height under dark and illuminated conditions. 2. Experimental process In this section, first, the processes of chemical cleaning and ohmic contact formation on p-Si substrates are described, after, GONiO nanocomposites film on the p-Si was spin coated at 3000 rpm for 30 s, and finally, the electrical measurements on the Ag/GO doped NiO/p-Si structure are introduced. 2.1. Chemical cleaning and contact formation For the fabrication of Ag/GO doped NiO/p-Si structure, p-type silicon (Si) wafer was used as substrate with (100) surface orientation, 400 mm thickness and 2e8 U-cm resistivity. The p-type Si wafer was chemically cleaned by using RCA cleaning procedure [35]. The cleaning processes leaved wafers with a thin oxide film which is known that an ohmic contact is required for realizing longlifetime operation of optical and electrical devices. The native oxide on the front surface of the substrate was removed in HF:H2O (1:10) solution and finally the wafer were rinsed in de-ionized water for 30 s. Then, low resistivity ohmic back contact to p-type Si (100) wafers was made by using Ag, followed by a temperature treatment at 570  C for 3 min in N2 atmosphere.

spectrometry (EDX) techniques. The p-Si (100) substrates were exposed to oxygen plasma cleaner to make the surface hydrophilic and dried. After, in order to prepare GO-NiO nanocomposites film on the p-Si was spin coated (6800 Spin Coater Series) at 3000 rpm for 30 s. This is followed by annealing the film at 50  C for 1 h in N2 atmosphere. The thickness of the GO-NiO nanocomposites film was measured using image of the cross section Scanning Electron Microscopy (SEM). The Schottky contacts have been formed by thermal evaporating about 50 nm thick Ag as dots with diameter of about 1.0 mm on the front surface of the GO-NiO/p-Si. Thus, the GONiO nanocomposites based diode, Ag/GO-NiO/p-Si structures was obtained by a spin coating and thermal evaporation technique. As can be seen Fig. 1, it shows the schematic diagram of the Ag/GONiO/p-Si structures based diode structure used in this study.

2.3. Electrical measurements The currentevoltage measurements of Ag/GO-NiO/p-Si heterojunction were performed at room temperature using a Keithley 2400 source meter. The capacitanceevoltage measurements were carried out with ST2826/A High Frequency LCR Meter. All measurements were carried out with the help of a microcomputer through an IEEE- 488 AC/DC converter card. In addition, the crosssectional SEM image of GO-NiO nanocomposites was examined by means of scanning electron microscope (SEM-Zeiss EVO 10LS) with energy dispersive X-ray spectrometry (EDX). The photo-response measurements of Ag/GO-NiO/p-Si heterojunctions were measured using a halogen lamb. The intensity of the light was controlled by solar power-meter (Model TM 206).

3. Results and discussion 3.1. Structural properties of GO doped NiO nanocomposite The structural and elemental analysis of the synthesized GO doped NiO layer were performed using scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDX). The SEM image of the GO doped NiO layer is shown in Fig. 2. Accordingly, graphene layers are naturally wrinkled and flexible, in contrast to graphite. The graphene layers are substantially thin and irregular according to Fig. 2(aeb). This situation was approved by energy dispersive spectroscopy, where nickel oxide particles at high densities were observed at certain sites. As can be seen in Fig. 2, the NiO nanoparticles are covered by GO layers. The coverage of GO on NiO nanoparticles change the dispersion of particles in GO doped NiO nanocomposites. This distributions have significant effects on the photo-response properties of GO-NiO/p-Si structure. Also, the GO-NiO structure was analyzed by energy dispersive X-ray spectrometry (EDX). The EDX spectrum of the film is shown in Fig. 3. As seen in Fig. 3, the X-ray (EDX) spectrum indicates the presence of C (61.01 wt %), O (34.32 wt %) and Ni (4.67 wt %) elements in GO-NiO structure.

2.2. Preparation of GO doped NiO nanocomposites The GO was prepared from extra pure graphite powder (Sigma Aldrich, 99.99%) according to improved Hummers. The GO was synthesized as powder, as we reported before in detail [36,37]. The GO doped NiO (C64O27Ni) material was characterized by the scanning electron microscopy (SEM) and energy dispersive X-ray

Fig. 1. Schematic representation of Ag/GO doped NiO/p-Si structure.

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Fig. 2. The cross-sectional SEM image of GO doped NiO structure.

3.2. Electrical properties of GO doped NiO/p-Si structure 3.2.1. The current-voltage (I-V) characteristics Fig. 4 shows the experimental semi-logarithmic currentevoltage (IeV) of the Ag/GO-NiO/p-Si structures obtained from under dark and illuminated conditions. As seen in Fig. 4, the Ag/GO-NiO/ p-Si structures exhibit rectifying behavior. The electrical properties of structure under both dark and light are determined from a fit of the linear region of the forward bias I-V plots. As shown in Fig. 4, the reverse current of the GO-NiO/p-Si structure increases with the illumination intensity. This means that the GO-NiO/p-Si structure are a photosensitive and show a photodiode behavior [38,39]. While currents increases exponentially with applied bias voltage in the intermediate voltage range, current curves deviate considerably

from linearity in the high bias region due to the effect of the series resistances. Thus, according to thermionic emission (TE) theory, the relation between the voltage (V) and current (I) can be written as [40e42];



qðV  IRS Þ qðV  IRS Þ 1  exp I ¼ I0 exp nkT kT

(1)

where Io is the saturation current derived from the straight line intercept of I-V curves at V ¼ 0 and expressed as;


qFbo Io ¼ AA* T 2 exp  kT

(2)

where q is the electronic charge, V is the applied bias voltage, k is

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Fig. 3. EDX spectrum of GO doped NiO structure.

the Boltzmann constant (1.3806
1023 J/K), n is the ideality factor which is a measure of conformity of the device according to thermionic emission, A is the contact area (7.85
103 cm2), A* is the effective Richardson constant and IRS is the voltage drop across the RS of the structure. Using Eqs. (1) and (2), equations of ideality factor (n) and barrier height (Fb) can be expressed as;

n¼

q kT




dV d ln I

 (3)

and

Fbo ¼


* 2 kT AA T ln q Io

(4)

Furthermore, the dependence of ideality factor from voltage can be written as;

nðVÞ ¼

Fig. 4. Forward and reverse bias currentevoltage characteristics of the Ag/GO doped NiO/p-Si structure in dark and under light source.

qV kT lnðI=I0 Þ

(5)

Using Eqs (3) and (4), according TE theory, the values of the ideality factor (n) and the barrier height (Fb) obtained from I-V measurements were found as 4.52 and 0.903 eV for dark and 4.38 and 0.887 eV under light, respectively. Also these values are shown in Table 1. As shown, the values of ideality factors and barrier heights have changed in dark and under light source. That is, the ideality factors and barrier heights obtained from dark are higher than under light source. The decrease in ideality factors and barrier heights is due to the photo-generated charge carriers under light source (white light illumination). The light source the rate of separation of carrier charge densities in depletion region at forward biases voltage and in turn, the current of the structures are

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Table 1 The some main parameters for the Ag/GO-NiO/p-Si structure in dark and under light source at room temperature. Parameter

Under dark conditions

From forward bias IeV characteristics Barrier height, Fb (eV) 0.903 Ideality factor, n 4.52 Saturation current (A) 1.66
1010 From reverse bias IeV characteristics Barrier height, Fb (eV) 0.896 Ideality factor, n 1.044 Saturation current (A) 2.19
1010 From Cheung's method, dV/d(lnI) vs I Series resistance, Rs (kU) 43.951 Ideality factor, n 4.32 H(I) vs I Series resistance, RS (kU) 41.513 Barrier height, Fb (eV) 0.445 From Norde's method Series resistance, RS (kU) 140.816 Barrier height, Fb (eV) 1.047 From CeV characteristics Barrier height, FCV (eV) 1.380

Under light source 0.887 4.38 3.12
1010 0.798 1.043 9.83
109 28.216 4.87 26.188 0.402 128.068 1.020 1.429

increased suddenly and this causes a decrease in the ideality factors and barrier heights of the hetero structure. The higher values of ideality factor obtained from dark and under light source are attributed to the presence of GO-NiO nanocomposite layer, the existence of in homogenities barrier height, series resistance, and the presence of interface densities [43e46]. To explain the current conduction mechanism of the GO-NiO/pSi structure, ln(I)- ln(V) plots and semilog reverse-bias currentvoltage characteristics of the Ag/GO-NiO/p-Si structure were plotted in Fig. 5 (a)-(b), respectively. As can be in Fig. 5 (a), the ln(I)ln(V) curves for dark and illuminated intensities (30 mW/cm2) have three distinct linear regions with different slopes which were analysed by I ¼ AV m relation. Here m is any constant which determines the charge conduction mechanism. The values of m obtained from the slope of the ln(I)- ln(V) plots for first region, second region and third region were found to be 1.240, 5.128, 4.237 in dark and 1.465, 5.489, 4.020 at 30 mW/cm2 illuminated intensity, respectively. In the first region, the trap-charge limited conduction is dominant. In the second region, the slope of the ln(I)- ln(V) curves are larger than two and such behavior can be explained a super quadratic behavior, which is caused by the low concentration of charge carriers. Also, the potential barriers are lowered with increasing bias voltages. In region III, due to the strong electron injection, the electrons escape from the traps and contribute to the space charge current [47e49]. Furthermore, we have considered the following equation with RS ¼ 0 given as [50e52].


I qV ¼ I0 exp ½1  expðqV =kTÞ nkT

Fig. 5. (a) The Ln(I)-Ln(V) curves and (b) Semi-logarithmic I/[1exp(qV/kT)]-V curves of the Ag/GO doped NiO/p-Si structure in dark and under light source, respectively.

(6)

By using Eq. (6), the semilog reverse bias I/[1exp(qV/kT)] versus voltage curves are drawn from 0.00 to 2.20 V in Fig. 5 (b) for dark and illumination conditions. The linearity of the curves in the low-voltage region is improved by means of this normalization method by Rhoderick and Williams [41]. Using Eq. (6), ideality factor (n) can be expressed as;

n¼

q kT


d ln

dV



(7)

I 1expðqV kT Þ

According Fig. 5(b), as seen in Table 1, the forward bias barrier heights and ideality factors obtained from dark are larger than the

reverse bias barrier heights and ideality factors obtained from illumination conditions. Also, the values of forward bias barrier heights are larger than the under reverse bias barrier heights. This differences are due to the saturation current densities [52e54]. These states can be attributed to patch interfaces or to lateral inhomogeneities of the barrier heights [54e56]. The values of series resistances (RS) are very important parameters of GO-NiO/p-Si structures that influences the electrical properties of devices. Series resistance changes throughout the bias voltage regions and resistance is more effective on current-voltage characteristics due to larger voltage drop in this region. Because, the down ward concave curvature of the I-V plots at high voltages is caused by the presence of the effect of series resistance (RS). There

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are various techniques to calculate series resistance. In this study, the values of series resistance have obtained using Cheung and Cheung [57] and Norde [58] methods. According to ref. [57], Cheung functions can be written as follows:

shows the experimental F(V)-V plots of the Ag/GO-NiO/p-Si structure in dark and under source light. According to Norde function [58], the barrier height and series resistance values can be calculated from following equations;

dV kT ¼ Rs I þ n dðlnIÞ q

Fb ¼ FðV0 Þ þ

(8)

and



kT I ln ¼ IRS þ nFb HðIÞ ¼ V  n * 2 q AA T

RS ¼ (9)

where IRs is the voltage drop across series resistance of structure, n is the ideality factor and Fb is the barrier height. Eq. (8) should be a straight line with the intercept and slope giving ideality factor (n) and series resistance (RS) values, which this dates and values is shown in Fig. 6. Thus, firstly, we were calculated the values of barrier height, ideality factor and series resistance using Cheung functions [57]. Using expressions Eq. (8) and Eq. (9), from Figs. 6 and 7, experimental dV/dln(I) vs. I and H(I) vs. I plots are presented under dark and source light for Ag/GO-NiO/p-Si heterojunction, respectively. Using in Eq. (8), for Fig. 6 from the slope and intercept of dV/dln(I)-I plots, the RS and n values obtained as 43.951 kU and 4.32; 28.216 kU and 4.87 in dark under source light, respectively. In the same way, using in Eq. (9), for Fig. 7 from the slope and intercept of H(I)-I plots, the RS and Fb values obtained as 41.513 kU and 0.445 eV; 26.188 kU and 0.402 eV in dark under source light, respectively. As can be in Table 1, the series resistance values obtained in dark are higher than obtained from source light. Norde [58] have proposed another method to determine values of the series resistance and barrier height. The method modified by Norde method can be written as follows:

FðVo ; gÞ ¼

V

g




 kT IðVÞ ln q AA* T 2

(10)

where F(Vo) is the minimum point of the F(V)-V plot, g is an constant higher than the ideality factors obtained from in Fig. 4. Fig. 8

gn I

V0

g



kT q

kT q

(11)

(12)

where V0 and I are the bias voltage and current values, respectively. Using in Eqs. (11) and (12), according Norde's method, the RS and Fb values obtained as 140.816 kU and 1.047 eV; 128.068 kU and 1.020 eV for Ag/GO-NiO/p-Si structure in dark and under source light, respectively. It is clear shown that the barrier height and series resistance values obtained from Cheung's functions is lower than the one obtained from Norde functions. Because, Norde's functions are applied to the full forward bias region of the lnIeV characteristics of the junctions, while Cheung functions are only applied to the nonlinear region in high voltage region of the forward bias IeV characteristics [40,41,57,58]. 3.2.2. The capacitance-voltage (C-V) characteristics The analysis of capacitance-voltage characteristics are one of the principal properties of the electronic circuit structure. Fig. 9 (a and b) show the measured C-V and C2-V plots of Ag/GO-NiO/p-Si structure in dark and under source light, at 500 kHz frequency and room temperature, respectively. The C-V technique is another method to determine the barrier height from C-V dates with the main properties of the structure. As shown in Fig. 9 (a) and (b), CeV and C2-V plots are strongly connected on applied bias voltage. As shown, the C2eV curves is linear in the between 0.45 V and 0.95 V for both states. The C-V correlation of MS/MOS/MIS structures are given by Refs. [40,41];

1 2ðVR þ Va Þ ¼ C2 qεS NA A2

(13)

where C2-V plot can be also given by:

  d C 2 2 ¼ dV NA A2 qεS

(14)

where A is the area of the diode, εs is the permittivity of the semiconductor, VR the reverse bias, Va is diffusion, q is the electronic charge and NA is the acceptor doping density. The barrier height (FCV) from C-V dates can be written as follow;

FCV ¼ Vi þ

Fig. 6. Experimental dV/dln(I) vs. I plots characteristics of the Ag/GO doped NiO/p-Si structure in dark and under light source.


 kT kT N þ ln V  DFb ¼ Va þ EF  DFb q q NA

(15)

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi where DFb ¼ qEm =4pεs ε0 is the image force, Em ¼ 2qNA VD =εs εo is the maximum electric field, and EF is the Fermi energy ð¼ kT=qlnðNV =NA ÞÞ, Vi is the intercept point of V-axis from C2eV curve, Va is the diffusion potential ð¼ Vi þ kT=qÞ and NV is the effective density of states in the valance band. Using Eq. (15), the calculated barrier heights (FCV) of Ag/GO-NiO/p-Si structure are 1.380 and 1.429 eV under dark and light source, respectively. All values obtained from IeV and CeV measurements are given in Table 1. As can be seen in Table 1, the values of barrier heights obtained from C-V measurements under dark and light source are higher than those obtained from I-V measurements. That is, the barrier heights obtained from IeV and CeV measurements are different due to different nature of the CeV and IeV methods. The

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Fig. 7. H (I) vs. I plots of characteristics of the Ag/GO doped NiO/p-Si structure in dark and under light source.

0.99

0.97

0.95

F(V)

0.93

0.91

0.89

0.87

0.85

0.83 0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

Voltage (V) Fig. 8. F(V) vs. V plots of characteristics of the Ag/GO doped NiO/p-Si structure in dark and under light source.

different between barrier heights (FIV and FCV) can be explained existence of excess capacitance and barrier heights inhomogeneities [40,41,59]. Also, the direct current across the interfaces are exponentially dependent on barrier heights and the currents are sensitive to barrier distribution at the interface.

However, the capacitances are insensitive to potential fluctuations on a length scale of less than the space charge width that the capacitanceevoltage method averages over the whole area [59e62]. Therefore, the barrier height values obtained from C-V measurement are higher than that of the barrier height values

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Fig. 9. (a) The experimental capacitance-voltage and (b) reverse bias C2-V characteristics of the Ag/GO doped NiO/p-Si in dark and under light source.

obtained I-V measurements. 3.2.3. The energy distribution profile of interface state densities The interface states densities (NSS) of the Ag/GO-NiO/p-Si structure under dark and light source can be derived by using the Card and Schroder method [63,64] and can be expressed as;

NSS ðVÞ ¼

  1 εi ðnðVÞ  1Þ εs  q d WD

(16)

where WD is the space charge width (WD was also calculated CeV dates at 0.5 MH), NSS is the density of interface states, εo is the permittivity of free space (¼8.85
1014 F cm1), εs (¼3.8εo) and εi (¼11.8εo) are the permittivity of the semiconductor and interfacial layer and d is the thickness of the insulator layer, which the values of interfacial insulator layer thickness ðd ¼ εi εo A=Cmax Þ were found to be 3713 oA and 3557 oA under dark and light source using CeV dates at 500 kHz, respectively. Besides, the interface state energies (ESS) with respect to the top of the valance band (EV) at the surface of the semiconductor structure is given by Refs. [34,40,41].

ESS  EV ¼ qðFe  VÞ

(17)

where q is the electronic charge, V is the applied bias voltage and Fe is the effective barrier height that is given by Fe ¼ Fbo þ ð1  1=nÞV. As shown in Fig. 10, the energy distribution curves of interface states densities have apparent exponential increase from the mid gap of semiconductor towards the top of valance band of the Ag/GO-NiO/p-Si structure, and the interface states densities decreased with applied voltages. In Fig. 10, while the interface densities obtained from under light source has increased exponentially with bias from 9.54
1012 cm2eV1 in (0.840- EV)

eV to 2.66
1013 cm2eV1 in (0.605- EV) eV of Ag/nGO-NiO/p-Si structure, the interface densities obtained from dark has increased exponentially with bias from of 9.47
1012 cm2eV1 in (0.833- EV) to 2.66
1013 cm2eV1 for Ag/GO-NiO/p-Si structure. As shown in Fig. 10, there is an exponential increase in interface densities with a decrease in forward bias voltage. That is, there is a decrease in interface densities with increase in forward bias voltage. These states of interface densities is due to the number of photogenerated charges at interface of the diode [34,40,41].

4. Conclusion In this study, we prepared the GO-NiO nanocomposites by a modified hummer's method. After, we synthesized GO-NiO nanocomposites using chemical method and examined the structure and morphology of Ag/GO-NiO/p-Si structure. The SEM images indicated that the surface of the GO doped NiO film consists of the clusters formed with the coming together of the nanoparticles. The main electrical properties of the Ag/GO-NiO/p-Si structure was analyzed by using I-V and C-V characteristics in dark and under light source. Also, the energy density distribution profile of interface state densities was obtained from the forward bias IeV measurements by taking into account voltage dependent effective barrier height (Fe) and ideality factor (nV) for the Ag/GO-NiO/p-Si structure, and an exponential increase in interface state density is apparent from the midgap toward the top of the valance band. Such a graphene oxide doped nickel oxide nanocomposite layer not only prevents interdiffusion between metal and semiconductor, but also alleviates the electric field reduction issue in these devices. The obtained these experimental results showed that the diode with GO doped NiO interfacial layer can be used as a photodiode or in

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Fig. 10. The energy distribution profile of interface state densities obtained from the forward bias IeV characteristics of Ag/GO doped NiO/p-Si in dark and under light source.

optoelectronic circuits. Acknowledgement This work was supported by Kahramanmaras Sütçü Imam University Scientific Research Project Unit, Project numbers: 2015/373D). We would like to thank Kahramanmaras¸ Sütcü Imam University for financial support of the research program. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

[14] [15] [16]

[17] [18] [19] [20]

Yow-Jon Lin, Superlattices Microstruct. 88 (2015) 645. S.D. Sarma, S. Adam, E.H. Hwang, E. Rossi, Rev. Mod. Phys. 83 (2011) 407. Y.J. Lin, J.J. Zeng, H.C. Chang, Appl. Phys. A 118 (2015) 353. D. Sinha, J.U. Lee, Nano Lett. 14 (2014) 4660. A.K. Geim, K.S. Novoselov, Nat. Mater. 6 (2007) 183. V. Singh, D. Joung, L. Zhai, S. Das, S.I. Khondaker, S. Seal, Prog. Mater. Sci. 56 (2011) 1178. K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Science 306 (2004) 666. S. Park, R.S. Ruoff, Nat. Nanotechnol. 4 (2009) 217. A. Reina, X. Jia, J. Ho, D. Nezich, H. Son, V. Bulovic, M.S. Dresselhaus, J. Kong, Nano Lett. 9 (2009) 30. J.C. Delgado, J.M.R. Herrera, X. Jia, D.A. Cullen, H. Muramatsu, Y.A. Kim, T. Hayashi, Z. Ren, D.J. Smith, Y. Okuno, Nano Lett. 8 (2008) 2773. V.C. Tung, M.J. Allen, Y. Yang, R.B. Kaner, Nat. Nanotechnol. 4 (2009) 25. N. Li, Z. Wang, K. Zhao, Z. Shi, Z. Gu, S. Xu, Carbon 48 (2010) 255. ndez, D. Meneses-Rodríguez, V.J. Gonz A.L. Elías, A.R. Botello-Me alez, ~ oz-Sandoval, P.M. Ajayan, H. Terrones, D. Ramírez-Gonz alez, L. Ci, E. Mun M. Terrones, Nano Lett. 10 (2010) 366. M. Choucair, P. Thordarson, J.A. Stride, Nat. Nanotechnol. 4 (2009) 30. S. Li, D. Deng, Q. Shi, S. Liu, Microchim. Acta 177 (2012) 325. E. Rollings, G.H. Gweon, S.Y. Zhou, B.S. Mun, J.L. McChesney, B.S. Hussain, A.V. Fedorov, P.N. First, W.A. de Heer, A. Lanzara, J. Phys. Chem. Solids 67 (2006) 2172. W.S. Hummers, R.E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. R.M. Ma, X.L. Wei, L. Dai, H.B. Huo, G.G. Qin, Nanotechnology 18 (2007) 205. A.A. Yadav, E.U. Masumdar, J. Alloy. Compd. 509 (2011) 5394. R.M. Ma, X.L. Wei, L. Dai, H.B. Huo, G.G. Qin, Nanotechnology 18 (2007) 205e210.

_ Polat, M.A. Olgar, M. Tomakin, E. Bacaksız, Mat. Sci. € reli, I. [21] S. Yılmaz, S.B. To Semic. Proces. 60 (2017) 45. [22] D.P. Padiyan, A. Marikani, K.R. Murali, Phys. B Condens. Matter 357 (2005) 485. [23] D. Adler, J. Feinleib, Phys. Rev. B 2 (1970) 3112. [24] V. Stengl, S. Bakardjieva, T.M. Grygar, J. Bludsk, M. Kormunda, Chem. Cent. J. (2013) 7. [25] B. Zhao, J. Song, P. Liu, W. Xu, T. Fang, Z. Jiao, H. Zhang, Y. Jiang, Mater Chem. 21 (2011) 18792. [26] A.A. Hendi, F. Yakuphanoglu, J. Alloys Compd. 665 (2016) 418. [27] N.M. Khusayfan, J. Alloys Compd. 666 (2016) 501. [28] O. Çiçek, H. Uslu Tecimer, S.O. Tan, H. Tecimer, I. Orak, S¸. Altındal, Compos. Part B 113 (2017) 14. _ Uslu, [29] O. Çiçek, H. Uslu Tecimer, S.O. Tan, H. Tecimer, I. Orak, S¸. Altındal, I. Compos. Part B 98 (2016) 260. _ Uslu, Microelect. Eng. 149 (2016) 166. [30] A. Kaya, E. Marıl, S¸. Altındal, I. [31] Y. Zhua, H. Wanga, J. Zhub, L. Changc, L. Ye, Appl. Surf. Sci. 349 (2015) 27. [32] L. Chengpeng, H. Tingting, S. Xiaodong, W. Xiaoyi, S. Fenghua, G. Weimin, K. Lingxue, Polym. Degrad. Stab. 119 (2015) 178. [33] L. Shao, J. Li, Y. Guang, Y. Zhang, H. Zhang, Xi Che, Y. Wang, Mater. Des. 99 (2016) 235. € [34] S¸. Karatas¸, H. Ozerli, M.G. Aydin, J. Alloys Compd. 689 (2017) 1068. € [35] S¸. Karatas¸, S¸. Altındal, A. Türüt, A. Ozmen, Appl. Sur. Sci. 217 (2003) 250. _ lu, J. Nanoelect. Optoelect [36] I. Karteri, S¸. Karatas¸, M. Çavas¸, B. Arif, F. Yakuphanog 11 (2) (2016) 29. _ Karteri, S¸. Karatas¸, F. Yakuphanog lu, Appl. Surf. Sci. 318 (2014) 74. [37] I. [38] I. Beinik, M. Kratzer, A. Wachauer, L. Wang, Y.P. Piryatinski, G. Brauer, X.Y. Chen, Y.F. Hsu, A.B. Djuri_sic, C. Teichert, Beilstein J. Nanotechnol. 4 (2013) 208. [39] R.K. Gupta, A.A. Hendi, M. Cavas, A.A. Al-Ghamdi, O.A. Al-Hartomy, R.H. Aloraini, F. El- Tantawy, F. Yakuphanoglu, Phys. E 56 (2014) 288. [40] S.M. Sze, Physics of Semiconductor Devices, second ed., Willey & Sons, New York, 1981. [41] E.H. Rhoderick, R.H. Williams, Metal-semiconductor Contacts, Clarendon, Oxford, 1988. [42] Y. Aydogdu, F. Yakuphanoglu, A. Aydogdu, M. Sekerci, Y. Balci, I. Aksoy, Synth. Met. 107 (1999) 191. [43] N.N. Halder, P. Biswas, S. Kundu, P. Banerji, Sol. Energy Mater. Sol. Cells 132 (2015) 230. [44] L. Changshi, L. Feng, Comput. Mater. Sci. 107 (2015) 170. [45] J. Osvald, Solid-State Electron 50 (2006) 228. [46] Mustafa Ilhan, J. Mater. Electron. Devices 1 (2015) 15. [47] F. Yakuphanoglu, Sensors Actuators A 141 (2008) 383.

84 [48] [49] [50] [51] [52] [53] [54] [55] [56]

€ H. Ozerli et al. / Journal of Alloys and Compounds 718 (2017) 75e84 L.E. Dickens, IEEE Trans. Microw. Theor. Tech. 15 (1967) 101. F. Yakuphanoglu, B. Filiz S¸enkal, Polym. Engıneerıng Scıence 50 (2010) 929. M. Missous, E.H. Rhoderick, Electron. Lett. 22 (1986) 477. A. Bobby, N. Shiwakoti, S. Verma, P.S. Gupta, B.K. Antony, Mater. Sci. Sem. Proces. 21 (2014) 116. I. Orak, M. Toprak, A. Turut, Phys. Scr 89 (2014) 115810. R.T. Tung, Mater Sci. Eng. R. 35 (2001) 1. J.P. Sullivan, R.T. Tung, M.R. Pinto, W.R. Graham, J. Appl. Phys. 70 (1991) 7419. G.P. Ru, R.L. Van Meirhaeghe, S. Forment, Y.L. Jiang, X.P. Qu, S. Zhu, B.Z. Li, Solid State Electron 49 (2005) 606. _ Orak, B. Tasyürek, T. Kilinç, A. Türüt, Mat. Sci. Sem. K. Ejderha, A. Zengin, I.

Procs 14 (2011) 5. [57] S.K. Cheung, N.W. Cheung, Appl. Phys. Lett. 49 (1986) 85. [58] H. Norde, J. Appl. Phys. 50 (1979) 5052. [59] M. Siad, A. Keffous, S. Mama, Y. Belkacem, H. Menari, Appl. Surf. Sci. 236 (2004) 366. lu, B.F. S¸enkal, J. Phys. Chem. C 111 (2007) 1840. [60] F. Yakuphanog € Metin, S¸. Aydog an, K. Meral, J. Alloy. Compd. 585 (2014) 681. [61] O. [62] M.L. Grilli, S¸. Aydogan, M. Yilmaz, Superlattices Microstruct. 100 (2016) 924. [63] H.C. Card, E.H. Rhoderick, J. Phys. D. 3 (1971) 1589. [64] D.K. Schroder, Semiconductor Material and Device Characterization, Wiley, London, 1998.