1-s2.0-S0038092X16001651-main.pdf

7/26/2019 1-s2.0-S0038092X16001651-main.pdf

1/7

Relationship between photovoltaic and diode characteristicparameters in the Sn/p-SiSchottky type photovoltaics

A. Ozkartal, C. Temirci

Department of Physics, Faculty of Science, Yuzuncu Yil University, 65080 Van, Turkey

Received 27 November 2015; received in revised form 8 February 2016; accepted 17 February 2016Available online 14 March 2016

Communicated by: Associate Editor Takhir M. Razykov

Abstract

In order to investigate relationship between photovoltaic and diode characteristic parameters, we fabricated four kinds of samples ofSn/p-SiSchottky type photovoltaics using surface treatment by anodic oxidation and chemical etching method. Diode and photovoltaiccharacteristics of the samples were determined from the currentvoltage measurements performed in dark and under illumination. Etch-ing time of front surface of the p-Sisubstrate inHFsolution used in the fabrication ofSn/p-SiSchottky type photovoltaics was found tobe very influential on diode and photovoltaic parameters. Especially, an etching time of 30 s showed a positive effect both on diode andphotovoltaic characteristic parameters. It was also observed that the characteristic parameters of the samples were affected negativelydepending on the over-etching time. More importantly, a close relationship between photovoltaic parameters (fill factor, conversion effi-ciency) and diode parameters (ideality factor, series resistance) was observed. 2016 Elsevier Ltd. All rights reserved.

Keywords: Photovoltaic; Schottky; Diode; Surface treatment

1. Introduction

During the fabrication of metal/semiconductorrectifying contacts, an oxide layer on the surface of inor-ganic semiconductors may form. Diode characteristicparameters such as ideality factor (n), barrier height Ub,series resistance (Rs) can be affected by the oxide layer

(Cowley and Sze, 1965; Card and Rhoderick, 1971; Sze,1981; Rhoderick and Williams, 1988). In other words, thecharacteristics of Schottky diode with an interface layermay not obey the ideal Schottky theory. In the Schottkydiode fabrication, effects of interface states on thecurrentvoltage characteristics had been investigated

previously by a controlled surface oxidation and removalof the surface oxide layer (Ziel, 1968). Interface states havea dominant role on contact characteristics of a metal/semiconductor rectifying structures. Thus, the photovoltaiccharacteristics of Schottky type photovoltaic can beinfluenced from the surface treatment. We had investigatedthe effect of surface treatment on diode characteristics in

Sn/p-Si Schottky diodes before (Temirci et al., 2001).However, the goal of the present study is to investigaterelationships between photovoltaic and diode characteristicparameters in Sn/p-Si Schottky type photovoltaics. Forthis reason, four kinds of Sn/p-Si Schottky typephotovoltaics were produced using anodic oxidationand chemical surface cleaning procedure together.The relationships between photovoltaic and diodeparameters such as fill factor, conversion efficiency,ideality factor, series resistance were interpreted as an

http://dx.doi.org/10.1016/j.solener.2016.02.056

0038-092X/2016 Elsevier Ltd. All rights reserved.

Corresponding author. Tel.: +90 544 804 39 54; fax: +90 432 225 1802.

E-mail address:[email protected](C. Temirci).

www.elsevier.com/locate/solener

Available online at www.sciencedirect.com

ScienceDirect

Solar Energy 132 (2016) 96102
http://dx.doi.org/10.1016/j.solener.2016.02.056mailto:[email protected]://dx.doi.org/10.1016/j.solener.2016.02.056http://crossmark.crossref.org/dialog/?doi=10.1016/j.solener.2016.02.056&domain=pdfhttp://dx.doi.org/10.1016/j.solener.2016.02.056mailto:[email protected]://dx.doi.org/10.1016/j.solener.2016.02.056http://-/?-

7/26/2019 1-s2.0-S0038092X16001651-main.pdf

2/7

influence of surface treatment by anodization-chemicaletching process.

2. Experimental procedure

P-typeSiwafer with (100) orientation and resistivity of

110X

cm was used to fabricate Sn/p-Si contacts. Thewafer was chemically cleaned using the standard RCA pro-cedure (10-min boil in NH4+ H2O2+ 6H2O followed by a10-min boil in HCl + H2O2+ 6H2O) and etched withdilute HF:H2O (1:10) for 30 s to remove the native oxidelayer on the surface. Before each step, the wafer was rinsedin deionized water with a resistivity of 18 MX. Then it wasdried under N2 atmosphere and inserted into a vacuumcoating unit for metallization. The ohmic contact wasmade by evaporating Al on the back surface of the sub-strate, followed by a temperature treatment at 580 C for3 min in N2 atmosphere. The wafer was cut into fourpieces with a dimension of about 5 mm 5 mm. A piece

of them was immediately inserted into the evaporationchamber for forming the reference Sn/p-SiSchottky typephotovoltaics. This sample was called S0 (the referencesample). Before Schottky contact formation, the front sur-faces of the other samples with ohmic back contacts wereanodized in 0.1 M KOH electrolyte at a current densityof 1.0 mA/cm2 under constant current condition and atroom temperature. The details of the anodization processhave been presented previously (Saglam et al., 1997;Temirci et al., 2001). The second sample has been etchedfor 30 s with %10 hydrofluoric (HF) acid solution afteranodic oxidation process using 0.1 M potassium hydroxide

(KOH) solution, and the sample was named as S30. Thethird and fourth samples have also been etched using HFsolution of %10 with the etching periods of 60 and 75 safter the anodic oxidation process using 0.1 M KOH solu-tion and they have been named as S60 and S75, respec-tively. All of the anodization process of the samples wasperformed at a constant current of 1 mA/cm2 and contin-ued up to 21 V. Anodization and etching processes wererepeated several times. Finally each sample was insertedinto the evaporation chamber and Sn evaporated on thefront surface of them with a thickness of about 80 nm.Film thickness of the top contact was controlled by thefilm thickness monitoring system in the vacuum coaterunit. First, reference sample was produced without per-forming anodic oxidation process. The others were pro-duced using anodization and etching process withvarious etching period. Thus, we produced Sn/p-Siphoto-voltaic samples which have various interfacial layers. Allevaporation processes were performed in a vacuum coatingunit at about 105 Torr. The currentvoltage (IV) mea-surements of the samples were carried out using a Keithley6487 Picoammeter/Voltage source at room temperature.Diode measurements were performed in the dark. Thephotovoltaic measurements were carried out under an illu-mination of 100 mW/cm2 and AM1.5, using a solar

simulator.

3. Results and discussion

The IVmeasurements were performed of the samplesat room temperature, in dark and under illumination inorder to find out diode and photovoltaic characteristics,respectively. The current data obtained from IVmeasure-

ments in dark and under illumination have been convertedto the current value per unit area. The IVplots under illu-mination and in dark were given at the same graph in orderto see clearly the photovoltaic effects of the produced Sn/p-SiSchottky type photovoltaics (Figs. 14). As can be seenfromFigs. 14, all of the samples show a rectifier behaviorand exhibit a photovoltaic effect under illumination. Pho-tovoltaic effects of the samples reveal themselves especiallyat the case of reverse bias.

The IV graphs (Figs. 14) showing a rectifier featuremeans that they comply with simple thermionic emissiontheory (TE). According to theTE, the forward bias currentof a rectifier device must be exponential and it can be

expressed as (Ziel, 1968; Sze, 1981; Rhoderick andWilliams, 1988):

I Ioexp qV

nkT

1 exp

qV

kT

1

where

Io ART2 exp

qUbo

kT

2

is called saturation current, q is electronic charge, V isapplied voltage,kis the Boltzmanns coefficient,Tambient

temperature in Kelvin and was taken as 300 C, A is thediode area, Ubo is the barrier height at the zero bias and

Fig. 1. Forward and reverse bias currentvoltage characteristics of theSn/

p-Si(Ref. sample:S0) Schottky type photovoltaics at room temperature in

dark and under illumination.

A. Ozkartal, C. Temirci / Solar Energy 132 (2016) 96102 97
http://-/?-

7/26/2019 1-s2.0-S0038092X16001651-main.pdf

3/7

R* represents Richardsons constant, which is equal to32 A cm2 K2 for p-Si.

For qV > 3kT, the second term in brackets on the rightside of Eq. (1) is negligible, and the equation can be re-written as follows:

I Io exp qV

nkT

3

n is named as ideality factor and it is a measure of

conformity of the diode to pure thermionic emission and

is determined from the slope of the straight line region ofthe forward bias lnIVcharacteristics through the relation,

n q

kT

dV

dlnI 4

In the case of an ideal contact (MS), the value of idealityfactor of a rectifier contact must be equal to 1 or at least

very close to 1 (Temirci et al., 2001). But, experimentalresults of ideality factor often show a deviation from thetheory. This situation can be originated from the effect ofthe bias voltage drop across the interfacial layer. Therefore,if ideality factor is greater than 1, it can be said that diodeis nonideal. Ideality factor is usually taken into account tofind out IV relationship of nonideal diode behaviors(Cheung and Cheung, 1986). The value of barrier heightis calculated from Eq. (2) as

qUbo kTln ART2

Io

5

Using Eqs.(4) and (5), the values of ideality factor andbarrier height were obtained from the IVdata of the sam-ples, respectively. The highest value of 0.8 eV for the bar-rier height has been obtained in the S0 sample. Thecontacts in theS0 sample have higher barrier height valuesthan those of the others. Besides this, they have relativelyhigh ideality factor values. These indicate that there maybe a native oxide layer between tin and silicon interface.Thus, the contacts of S0 sample have obeyed a metal-interfacial layer-semiconductor (MIS) configuration ratherthan a metalsemiconductor (MS) structure. However, thecontacts ofS30 sample have smaller values of ideality fac-tor than the others. This indicates that they are close to the

ideal diode in terms of their characteristics. Ideality factor

Fig. 2. Forward and reverse bias currentvoltage characteristics of theSn/p-Si (sample S30) Schottky type photovoltaics at room temperature indark and under illumination.



98 A. Ozkartal, C. Temirci / Solar Energy 132 (2016) 96102

7/26/2019 1-s2.0-S0038092X16001651-main.pdf

4/7

values ofS60 and S75samples are greater than those ofS0andS30 samples, and barrier height values ofS60 and S75samples are lower than those of the S0and S30sample. Wecan deduce that etching process shows positive effect whenetching time is 30 s. In addition, when the etching time isincreased (for a period of 60 and 75 s), diode characteristics

are affected negatively from over-etching process. That is,over-etching process has lead to distortion of the interfaceof the contacts ofS60andS75. The ideality factor values ofthe produced samples greater than 1 indicates that we musttake into account the series resistance in the calculations.To check the results obtained from IVdata and to deter-mine the series resistance value of the samples, we can rear-range Eq. (1) by considering a voltage drop across thediode due to series resistance (Cheung and Cheung, 1986),

I Io exp qVIRs

nkT

6

whereIRsterm is the voltage drop across the diode due toseries resistance. We can derive the Cheungs functionsusing Eq.(6)as follows (Cheung and Cheung, 1986):

dV

dlnI

nkT

q IRs 7

HI V nkT

q

IRs 8

HI nUb IRs 9

Eq. (7) is a linear equation and thus it should give astraight line for the data of the downward curvature regionof the forward biasIVcharacteristics. So, the slope and y-

axis intercept of a plot ofdV/d(ln I) versus Iwill give Rsand nkT/q, respectively. According to Eq. (9), a plot ofH(I) versus Iwill also give a straight line and y-axis inter-cept of the plot will give nUb. The slope of this plot alsoprovides a second determination ofRs, which can be usedto check the consistency of Cheung and Cheungsapproach. Only two graphs associated with these functionsare given here as Figs. 5 and 6.

Barrier height value for a metal/semiconductor rectifiercontact varies with the applied voltage under the forwardbias condition. The potential across the interfacial layervaries with the bias. This implies that interface chargemight be changed with the bias. Since interface chargemay be changed as a result of the applied voltage, barrierheight may be modified. Therefore, an additional barrierincrease in the forward bias comes from the potentialchange across the interfacial layer (Ayyildiz et al., 2001).

As can be seen fromTable 1, an effective value of barrierheight (qUb) has been obtained at the range from 0.70 to0.80 eV for the reference sample (sample S0). Furthermore,the values of ideality factor of the reference sample (S0)Sn/p-SiSBDs range from 1.12 to 1.19. For all of the dots ofthe sample S30, whose anodic oxide layer formed on p-Siwas removed by etching for 30 s with HF:H2O (1:10) solu-tion (the passivation method), effective values of barrier

height (qUb) have ranged from 0.74 to 0.75 eV. The ideality

factor values of the dots of this device have ranged from1.05 to1.08. For the samples S60 and S75, the values ofbarrier height (qUb) have ranged from 0.55 to 0.59 eVand from 0.58 to 0.59 eV, respectively. The ideality factorvalues of the same samples range from 1.29 to 1.30 andfrom 1.19 to 1.29, respectively. The lowest and the highestresistance values were determined as 0.17 X and 42.21 X forthe dot 1 of the samples S60and S0, respectively.

The average values of ideality factor were calculated as1.16, 1.06, 1.30, 1.24 for the four samples ofS0, S30, S60and S75, respectively. Conversion efficiency for each pho-tovoltaic is given inTable 1. These values are understoodto be comparable to those of the literature (Ji andAnderson, 2005; Soylu and Yakuphanoglu, 2011;Hussain and Rahman, 2015; Halder et al., 2015). More effi-

cient photovoltaics, of course, could be produced using

Fig. 5. ExperimentaldV/d(ln I) versus Iplots ofSn/p-Sirectifier contactsfor sample S30.

Fig. 6. ExperimentalH(I) versus Iplots ofSn/p-Sirectifier contacts forsample S30.

http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-

7/26/2019 1-s2.0-S0038092X16001651-main.pdf

5/7

various techniques (Razykov et al., 2011; Parida et al.,2015; Da and Xuan, 2015; Xi et al., 2015). However, it isalso very important to disclose experimentally the relation-ships between diode and photovoltaic parameters. It isunderstood from the obtained numerical data and the plot-ted graphs that the devices ofS30 sample have better bothdiode and photovoltaic characteristics than the others. So,we can say that if a sample has a better diode characteristicit has a better photovoltaic characteristic. For determiningphotovoltaic properties of the produced samples, IVmea-surements were performed by a solar simulator under

AM1.5 and 100 mW/cm2

illumination. The currentvolt-age curves under illumination are given in Figs. 710 indetail. After determining the characteristics such as shortcircuit current Isc and open circuit voltage Voc fromFigs. 710, the values of fill factor (FF) and conversion

efficiency (g) of the samples can be calculated by usingEqs.(10) and (11), (Fonash, 2010),

FFVmIm

VocIsc10

where Vm and Im are the maximum voltage and maximumcurrent, respectively corresponding to the maximum out-put power. Voc and Isc are named open circuit voltageand short circuit current, respectively. FF is the ratio ofthe rectangular area formed by the multiplication of VmandI

mto the rectangular area formed by the multiplication

ofVoc and Isc.FFmust obey to the limitation ofFF6 1, asbased on recognition. A second parameter of a photo-voltaic device is the conversion efficiency g, and it is givenas follow,

Table 1Electrical and photovoltaic characteristic values, obtained from IVdata for the samples ofS0, S30, S60 and S75.

Samples n(IV) n(Cheung) Ub (eV)(IV) Ub (eV)(Cheung)

Rs (X)(dV/dln I)I

Rs (X)(H(I)I)

Fillfactor (FF)

Efficiency(%) (g)

S0(reference) d1 1.12 1.13 0.80 0.76 27.32 42.21 0.48 0.13d2 1.18 1.20 0.70 0.76 19.51 41.37 0.56 0.10d3 1.16 1.15 0.76 0.76 39.77 19.21 0.60 0.13

d4 1.19 1.21 0.76 0.75 35.30 32.88 0.45 0.09

S30(30 sn etch) d1 1.08 1.07 0.74 0.64 0.32 0.40 0.62 0.66d2 1.05 1.08 0.74 0.62 0.20 0.32 0.63 0.64d3 1.05 1.08 0.75 0.61 0.18 0.27 0.57 0.68d4 1.06 1.08 0.74 0.60 0.17 0.22 0.63 0.74

S60(60 sn etch) d1 1.30 1.31 0.55 0.62 0.17 0.17 0.48 0.28d2 1.29 1.32 0.62 0.60 0.35 0.38 0.58 0.33d3 1.30 1.33 0.59 0.59 0.23 0.25 0.48 0.32

S75(75 sn etch) d1 1.22 1.26 0.58 0.62 0.30 0.49 0.44 0.16d2 1.25 1.28 0.58 0.62 0.28 0.42 0.40 0.11d3 1.29 1.33 0.58 0.63 0.51 0.76 0.44 0.13d4 1.19 1.23 0.59 0.59 0.29 0.45 0.45 0.13

Fig. 7. The currentvoltage characteristics of the sample S0 at room

temperature under AM1.5, 100 mW/cm2

illumination.

Fig. 8. The currentvoltage characteristics of the sample S30 at room

temperature under AM1.5, 100 mW/cm2

illumination.


7/26/2019 1-s2.0-S0038092X16001651-main.pdf

6/7

g VmIm

Pin11

where Pin is the incoming photon power per surface area.FF and g values of the samples were calculated usingEqs.(10) and (11)withFigs. 710. Photovoltaic and electri-cal values of each device were given inTable 1, and meanvalues of them are given inTable 2. TheIscnotation, given

inTable 2, actually shows the current value per unit area.As seen from Table 1, the electrical and photovoltaicparameters have varied from device to device. However,variations of diodes and photovoltaic parameters for eachdevice are understood to be proportional to each other. Inaddition, it is clear fromTable 2that there is a relationshipbetween the changes of electrical and photovoltaic param-eters. Namely, according to the values ofTable 2, it seemsthat there is an inverse relationship between the values ofthe FF and the n. In addition, it seems that there is alsoan inversely proportional relationship between ideality fac-tor and conversion efficiency. Moreover, it is clear thatthere is an inverse proportion between the values of seriesresistance obtained using the Cheungs functions from thedark IV data and the values of FF. Furthermore, thereis also an inverse proportion between the values of seriesresistance and the values of efficiency. The relationshipsbetween series resistance and photovoltaic parameters areconsistent with those of the literature (Goetzberger et al.,1998). Recently, the relationship between some electricalparameters such as carrier concentration, mobility andphotovoltaic parameters have been studied using a hetero-

junction structure (Minami et al., 2016). In the presentstudy, the dependence of photovoltaic parameters (effi-ciency and fill factor) onto ideality factor and series resis-tance have been examined using Sn/p-Si Schottkystructure. Fig. 11 shows the mean currentvoltage

Fig. 9. The currentvoltage characteristics of the sample S60 at roomtemperature under AM1.5, 100 mW/cm2 illumination.

Fig. 10. The currentvoltage characteristics of the sample S75 at roomtemperature under AM1.5, 100 mW/cm2 illumination.

Table 2Mean values of the some electrical and photovoltaic characteristics of theSn/p-SiSchottky type photovoltaics for the samples ofS0, S30, S60 and S75.

Sample n Ub (eV) Isc (A) Voc(V) RS(X) (dV/dln I)I FF g(%)

S0(reference) 1.16 0.76 0.0009 0.23 30.47 0.52 0.11

S30(30 sn etch) 1.06 0.74 0.0050 0.22 0.22 0.61 0.68S60(60 sn etch) 1.30 0.59 0.0021 0.28 0.25 0.51 0.31

S75(75 sn etch) 1.24 0.58 0.0027 0.11 0.27 0.43 0.13

Fig. 11. Mean currentvoltage characteristics of each contact of thesamples of S0, S30, S60 and S75, at room temperature under AM1.5,

100 mW/cm2

illumination.

http://-/?-http://-/?-http://-/?-http://-/?-

7/26/2019 1-s2.0-S0038092X16001651-main.pdf

7/7

characteristics of contacts of each sample underillumination. The relationship between photovoltaic anddiode parameters of Sn/p-Si Schottky structures areshown clearly fromFig. 11. We can deduce from Fig. 11that if the values of ideality factor and series resistanceare higher, the values of fill factor and efficiency will be

lower.

4. Conclusion

We have investigated experimentally the relationshipbetween photovoltaic and diode parameters of four kindsof Sn/p-SiSchottky type photovoltaic samples using sur-face treatment by anodic oxidation and chemical etchingmethod. We found that there is a close relationshipbetween photovoltaic and diode parameters. In this con-text, the following results were obtained: The best charac-teristic value for the diodes and photovoltaics wasobtained with the sample S30, one of the four samples.

Moreover, we observed deterioration in characteristics ofdiode and photovoltaic for an etching time of 60 and75 s. More importantly, it was observed that fill factorand conversion efficiency has an inversely proportionalrelationship with ideality factor, as seen from Table 2andFig. 11. Similarly, fill factor and conversion efficiencyare also inversely proportional to series resistance. We havenot included interface states to this study. We believe that athorough investigation of this parameter can moreenlighten the relationships between diode and photovoltaiccharacteristics.

Acknowledgement

We would like to thank Yuzuncu Yl UniversityScientific Research Management Office for their fundingsupport.

References

Ayyildiz, E., Temirci, C., Bati, B., Turut, A., 2001. The effect of seriesresistance on calculation of the interface state density distribution inSchottky diodes. Int. J. Electron. 88 (6), 625633.

Card, H.C., Rhoderick, E.H., 1971. Studies of tunnel MOS diodes:interface effects in silicon Schottky diodes. J. Phys. D: Appl. Phys. 4,15891601.

Cheung, S.K., Cheung, N.W., 1986. Extraction of Schottky diodeparameters from forward current-voltage characteristics. Appl. Phys.Lett. 49 (2), 8587.

Cowley, A.M., Sze, S.M., 1965. Surface States and Barrier Height ofMetal-Semiconductor Systems. J. Appl. Phys. 36 (10), 32123220.

Da, Y., Xuan, Y., 2015. Effect of temperature on performance ofnanostructured silicon thin-film solar cells. Sol. Energy 115, 109119.

Fonash, S.J., 2010. Solar Cell Device Physics, second ed. Elsevier.Goetzberger, A., Knobloch, J., Voss, B., 1998. Crystalline Silicon Solar

Cells. John Wiley & Sons, West Sussex.Halder, N.N., Biswas, P., Kundu, S., Banerji, P., 2015. Au/p-Si Schottky

junction solar cell: effect of barrier height modification by InPquantum dots. Sol. Energy Mater. Sol. C 132, 230236.

Hussain, A., Rahman, A., 2015. Electrical and photovoltaic characteristicsof Ni/(n)Bi2S3Schottky barrier junction. Superlattices Microstruct. 80,3952.

Ji, C., Anderson, W.A., 2005. Poly-Si thin films by metal-induced growthfor photovoltaic applications. Sol. Energy Mater. Sol. C 85, 313320.

Minami, T., Miyata, T., Nishi, Y., 2016. Relationship between theelectrical properties of the n-oxide and p-Cu2O layers and thephotovoltaic properties of Cu2O-based heterojunction solar cells.Sol. Energy Mater. Sol. C 147, 8593.

Parida, B., Lim, G., Choi, J., Palei, S., Kim, K., 2015. Hydrogenpassivation effect on the conversion efficiency of Si solar cells by low-energy proton implantation. Sol. Energy 122, 486496.

Razykov, T.M., Ferekides, C.S., Morel, D., Stefanakos, E., Ullal, H.S.,Upadhyaya, H.M., 2011. Solar photovoltaic electricity: current statusand future prospects. Sol. Energy 85, 15801608.

Rhoderick, E.H., Williams, R.H., 1988. Metal-Semiconductor Contacts.Clarendon Press, Oxford.

Saglam, M., Turut, A., Nuhoglu, C., Efeoglu, H., Kilicoglu, T., Ebeoglu,M.A., 1997. Influences of thermal annealing, the electrolyte pH, andcurrent density on the interface state density distribution of anodicMOS structures. Appl. Phys. A 65, 3337.

Soylu, M., Yakuphanoglu, F., 2011. Photovoltaic and interface statedensity properties of the Au/n-GaAs Schottky barrier solar cell. ThinSolid Films 519, 19501954.

Sze, S.M., 1981. Physics of Semiconductor Devices, second ed. Wiley, NewYork.

Temirci, C., Bati, B., Saglam, M., Turut, A., 2001. High-barrier height Sn/p-Si Schottky diodes with interfacial layer by anodization process.Appl. Surf. Sci. 172, 17.

Xi, X., Chen, X., Zhang, S., Li, W., Shi, Z., Li, G., 2015. The investigationon the front surface field of aluminum rear emitter N-type silicon solarcells. Sol. Energy 114, 198205.

Ziel, A., 1968. Solid State Physical Electronics, second ed. Prentice-Hall,New Jersey.

http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0010http://refhub.elsevier.com/S0038-092X(16)00165-1/h0010http://refhub.elsevier.com/S0038-092X(16)00165-1/h0010http://refhub.elsevier.com/S0038-092X(16)00165-1/h0015http://refhub.elsevier.com/S0038-092X(16)00165-1/h0015http://refhub.elsevier.com/S0038-092X(16)00165-1/h0015http://refhub.elsevier.com/S0038-092X(16)00165-1/h0020http://refhub.elsevier.com/S0038-092X(16)00165-1/h0020http://refhub.elsevier.com/S0038-092X(16)00165-1/h0025http://refhub.elsevier.com/S0038-092X(16)00165-1/h0025http://refhub.elsevier.com/S0038-092X(16)00165-1/h0030http://refhub.elsevier.com/S0038-092X(16)00165-1/h0035http://refhub.elsevier.com/S0038-092X(16)00165-1/h0035http://refhub.elsevier.com/S0038-092X(16)00165-1/h0040http://refhub.elsevier.com/S0038-092X(16)00165-1/h0040http://refhub.elsevier.com/S0038-092X(16)00165-1/h0040http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0050http://refhub.elsevier.com/S0038-092X(16)00165-1/h0050http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0060http://refhub.elsevier.com/S0038-092X(16)00165-1/h0060http://refhub.elsevier.com/S0038-092X(16)00165-1/h0060http://refhub.elsevier.com/S0038-092X(16)00165-1/h0065http://refhub.elsevier.com/S0038-092X(16)00165-1/h0065http://refhub.elsevier.com/S0038-092X(16)00165-1/h0065http://refhub.elsevier.com/S0038-092X(16)00165-1/h0070http://refhub.elsevier.com/S0038-092X(16)00165-1/h0070http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0080http://refhub.elsevier.com/S0038-092X(16)00165-1/h0080http://refhub.elsevier.com/S0038-092X(16)00165-1/h0080http://refhub.elsevier.com/S0038-092X(16)00165-1/h0085http://refhub.elsevier.com/S0038-092X(16)00165-1/h0085http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0095http://refhub.elsevier.com/S0038-092X(16)00165-1/h0095http://refhub.elsevier.com/S0038-092X(16)00165-1/h0095http://refhub.elsevier.com/S0038-092X(16)00165-1/h0100http://refhub.elsevier.com/S0038-092X(16)00165-1/h0100http://refhub.elsevier.com/S0038-092X(16)00165-1/h0100http://refhub.elsevier.com/S0038-092X(16)00165-1/h0100http://refhub.elsevier.com/S0038-092X(16)00165-1/h0095http://refhub.elsevier.com/S0038-092X(16)00165-1/h0095http://refhub.elsevier.com/S0038-092X(16)00165-1/h0095http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0090http://refhub.elsevier.com/S0038-092X(16)00165-1/h0085http://refhub.elsevier.com/S0038-092X(16)00165-1/h0085http://refhub.elsevier.com/S0038-092X(16)00165-1/h0080http://refhub.elsevier.com/S0038-092X(16)00165-1/h0080http://refhub.elsevier.com/S0038-092X(16)00165-1/h0080http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0075http://refhub.elsevier.com/S0038-092X(16)00165-1/h0070http://refhub.elsevier.com/S0038-092X(16)00165-1/h0070http://refhub.elsevier.com/S0038-092X(16)00165-1/h0065http://refhub.elsevier.com/S0038-092X(16)00165-1/h0065http://refhub.elsevier.com/S0038-092X(16)00165-1/h0065http://refhub.elsevier.com/S0038-092X(16)00165-1/h0060http://refhub.elsevier.com/S0038-092X(16)00165-1/h0060http://refhub.elsevier.com/S0038-092X(16)00165-1/h0060http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0055http://refhub.elsevier.com/S0038-092X(16)00165-1/h0050http://refhub.elsevier.com/S0038-092X(16)00165-1/h0050http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0045http://refhub.elsevier.com/S0038-092X(16)00165-1/h0040http://refhub.elsevier.com/S0038-092X(16)00165-1/h0040http://refhub.elsevier.com/S0038-092X(16)00165-1/h0040http://refhub.elsevier.com/S0038-092X(16)00165-1/h0035http://refhub.elsevier.com/S0038-092X(16)00165-1/h0035http://refhub.elsevier.com/S0038-092X(16)00165-1/h0030http://refhub.elsevier.com/S0038-092X(16)00165-1/h0025http://refhub.elsevier.com/S0038-092X(16)00165-1/h0025http://refhub.elsevier.com/S0038-092X(16)00165-1/h0020http://refhub.elsevier.com/S0038-092X(16)00165-1/h0020http://refhub.elsevier.com/S0038-092X(16)00165-1/h0015http://refhub.elsevier.com/S0038-092X(16)00165-1/h0015http://refhub.elsevier.com/S0038-092X(16)00165-1/h0015http://refhub.elsevier.com/S0038-092X(16)00165-1/h0010http://refhub.elsevier.com/S0038-092X(16)00165-1/h0010http://refhub.elsevier.com/S0038-092X(16)00165-1/h0010http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005http://refhub.elsevier.com/S0038-092X(16)00165-1/h0005

1-s2.0-S0038092X16001651-main.pdf

Documents

Transcript of 1-s2.0-S0038092X16001651-main.pdf