Research Article Zn Electrodeposition on Single-Crystal GaN ......Research Article Zn...

Research ArticleZn Electrodeposition on Single-Crystal GaN(0001) SurfaceNucleation and Growth Mechanism

Fei Peng12 Shuang-Jiao Qin2 Yu Zhao2 and Ge-Bo Pan2

1Nano Science and Technology Institute University of Science and Technology of China Suzhou 215123 China2Suzhou Institute of Nano-Tech and Nano-Bionics Chinese Academy of Sciences Suzhou 215123 China

Correspondence should be addressed to Ge-Bo Pan gbpan2008sinanoaccn

Received 30 September 2015 Revised 13 January 2016 Accepted 14 January 2016

Academic Editor Sheng S Zhang

Copyright copy 2016 Fei Peng et alThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The electrochemical deposition of zinc on single-crystal 119899-type GaN(0001) from a sulphate solution has been investigated onthe basis of electrochemical techniques including cyclic voltammetry chronoamperometry and Tafel plot The morphology andcrystal structure of zinc deposits have been characterized bymeans of scanning electronmicroscopy X-ray diffraction and energy-dispersive X-ray analysis The result has revealed that the deposition of Zn on GaN electrode commenced at a potential of minus112 Vversus AgAgCl According to the Tafel plot an exchange current density of sim0132mA cmminus2was calculated In addition the currenttransient measurements have shown that Zn deposition process followed the instantaneous nucleation in 10mM ZnSO

4

+ 05MNa2

SO4

+ 05M H3

BO3

(pH = 4)

1 Introduction

The electrodeposition of zinc (Zn) and its alloys are ofpractical and industrial importance due to their excellentanticorrosive properties [1ndash5] Diverse factors such as pH [6]concentration of Zn ions [7] anions [8] and organic additives[9] are found to influence theZn electrodepositionHoweverit is noted that previous studies of Zn electrodeposition aremostly performed on metal electrodes (eg steel [5] nickel[10] platinum [11] copper [12] gold [13] and aluminum [14])To the best of our knowledge no report has described theZn electrodeposition on semiconductor electrodes althoughthey are of interest in modern technologies such as light-emitting diodes and microelectromechanical systems [15ndash17] This is due to complicated thermodynamics and kineticsat metalsemiconductor interface induced by unique chargetransfer band structure and weak metal-substrate interac-tion

On the other hand gallium nitride- (GaN-) based mate-rials with a wide band gap have recently attracted greatattention because of their wide applications in advancedoptoelectronic devices [18ndash20] Besides physics applicationsthere is an increasing interest in electrochemistry field due

to their unique physicochemical properties For instancePt nanoparticle-modified GaN was found to have potentialapplications in catalysis and sensors [21 22] Pd-SGaNwas a very efficient and recycled green catalyst for Heckreaction [23] We have demonstrated that GaN might be anelegant alternative catalyst support similar toWO

3

TiO2

andZnO [24ndash26] They have shown excellent chemical stabilitylarge potential window for water electrolysis good electricconductivity and low background current

Herein a study of the electrodeposition of Zn onsingle-crystal 119899-type GaN(0001) electrode is presented Theelectrochemical reduction of Zn2+ from sulphate solutionwas investigated by basic electrochemical analysis includingcyclic voltammetry (CV) chronoamperometry (CA) andTafel plot The morphology and crystal structure of Zndeposits were characterized by means of scanning electronmicroscopy (SEM) X-ray diffraction (XRD) and energy-dispersive X-ray analysis (EDAX)

2 Material and Methods

Single-crystal 119899-type GaN(0001) substrates were grown onsapphire(0001) by a hydride vapor phase epitaxy The GaN

Hindawi Publishing CorporationInternational Journal of ElectrochemistryVolume 2016 Article ID 3212703 8 pageshttpdxdoiorg10115520163212703

2 International Journal of Electrochemistry

layer was 5 120583m thick Si-doped and with a carrier concentra-tion of 4 times 1018 cmminus3 Before each experiment the workingelectrode ofGaNwas cleanedwith ultrasonication in acetoneethanol and distilled water successively for 15min The Ptwires (1mm in diameter) were used as counter electrodes

Zinc sulphate (ZnSO4

) boric acid (H3

BO3

) sodiumsulphate (Na

2

SO4

) ethanol and acetone were of analyticalgrade and purchased from Sinopharm Chemical ReagentCo Ltd The electrolyte used in the present study was10mM ZnSO

4

+ 05M H3

BO3

+ 05M Na2

SO4

if it was notmentioned All the solutions were prepared by using Milli-Qwater (gt18MΩ) and all the reagents were used as received

The electrochemical experiments used a standard three-electrode cell arrangement and were undertaken with aCHI 660D potentiostatgalvanostat (Shanghai ChenHua CoLtd) The distance between working and counter electrodeswas about 1 cm The geometric area of GaN in contact withthe electrolyte was 05 cm2 All the potentials were reportedwith respect to a saturated AgAgCl electrode (0197V versusNHE)

The morphology of Zn deposits was investigated byscanning electron microscopy (Hitachi S4800) The X-raydiffraction (XRD) patterns were recorded on a Bruker D8Advance Powder X-Ray Diffractometer at a scanning rate of002∘ sminus1 in the 2120579 range 20 to 80∘ using Cu-Ka radiation(120582 = 15406 A)The energy-dispersiveX-ray analysis (EDAX)was performed on a Quanta 400 FEG SEM at 10 KV

3 Results and Discussion

In principle electrochemical nucleation involves the diffu-sion and charge transfer across the electrolyteelectrode inter-face In comparison with metal electrodes the deposition onsemiconductor electrodes ismore complicatedThis ismainlydue to the unique band structure of semiconductors whichaffects both thermodynamics and kinetics of depositionprocessesThe existence of Zn(Π) in 05MNa

2

SO4

and 05MH3

BO3

solution is generally considered to be Zn2+ due to itsstability The reduction process of Zn2+ can be expressed by

Zn2+ + 2eminus = Zn (1)

The Femi level is close to the conduction band due tothe high doped concentration Figure 1 shows the energyband diagram of the 119899-type GaNelectrolyte interface Itcan be seen that there are two sections For simplicity theredox couple is considered as energy states of the Gerischermodel of energy levels in the right side The midpointbetween the reduction and oxidation states corresponds tothe equilibrium potential 119864OR which is equivalent to aFermi level of a redox system

119864OR = 119864120579

OR + kT ln(119888ox119888red

) (2)

Theband energy ofGaNwas cited from the literature [27]When GaN was in contact with electrolyte the band energywould bend upward More importantly the Fermi energyof semiconductor and solution is equal at the electrostatic

GaN Electrolyte

015

345 9

756

453

150EF EOR

Dred

Dox

NH

EE

(eV

)

Vacu

umE

(eV

)

minus75minus6

minus45minus3

minus15

minus3minus15EC

EV

Figure 1 The energy band diagram for the 119899-type GaNelectrolyteinterface

minus16 minus12 minus08 minus04 00 04minus3

minus2

minus1

0

1

2

3

Potential (V)

OCP

minus095V

minus112V

minus128V

Curr

ent d

ensit

y (m

A cm

minus2)

05M Na2SO4 + 05 H3BO3

10mM ZnSO4 + 05M Na2SO4 + 05 H3BO3

Figure 2 Cyclic voltammograms of GaN electrode at the scan rateof 10mV sminus1

equilibrium condition As a result a space charge layer (SCL)was formed at the interface between semiconductor andsolution which is equivalent to the built-in potential formedat a Schottky junction [27]

Figure 2 presents typical CVs of GaN electrode in 05MH3

BO3

+ 05M Na2

SO4

solution with and without 10mMZnSO

4

at a scan rate of 10mVs The Open Circuit Potential(OCP) was about 018 V In the first cycle the cathodiccurrent started to increasewhen the potential reachedminus112Vindicating the beginning of Zn deposition Moreover anobvious cathodic reduction peak at potential ofminus128V can beobserved As described in the literatures [28 29] the reduc-tion proceeds in a single step (peak at minus128V) associatedwith the reduction of Zn(II) ions to Zn(0) No additionalpeaks are observed before overpotential deposition of Znindicating that no underpotential process occurs This ismainly due to the weak interaction between Zn depositand GaN On the reverse scan the anodic stripping peak isobserved at a potential of minus095V due to the dissolution ofZn In the second cycle the Zn deposition on GaN electrodecommencedmore positive than that of first one because someZn nuclei were still present on the electrode surface

International Journal of Electrochemistry 3

30 40 50 60 70 80 90

Inte

nsity

(au

)

GaN

(100)

(101)

(102)

GaN

(004)(112)(201)

(103)(110)

2120579 (deg)

(a)

05 10 15 20

Inte

nsity

(au

)

Energy (keV)

NO

Zn

Ga

(b)

Figure 3 (a) X-ray patterns and (b) EDAX spectra of Zn deposits

minus14 minus12 minus10 minus08 minus06 minus04minus4

minus3

minus2

minus1

0

1

2

3

4

5

Potential (V versus AgAgCl)

Curr

ent d

ensit

y (m

A cm

minus2)

5mVs10mVs

20mVs50mVs

(a)

2 3 4 5 6 708

10

12

14

16

18

20

22

minusj

(mA

cmminus2)

12 (mVs)

(b)

Figure 4 (a) Cyclic voltammograms for Zn deposition on GaN at different scan rates (b) A fitted line plot for the current density of cathodicpeak versus the square root of the scan rate

Figure 3(a) displays the XRD patterns of Zn deposits onGaN The deposition potential is minus14 V and the depositiontime is 7200 s The thickness of the Zn deposits is about400 nm The XRD pattern revealed five characteristic peaksat 2120579 = 389

∘ 432∘ 543∘ 701∘ and 706∘ which areattributed to the Zn diffraction peaks of the (100) (101)(102) (103) and (110) planes (JCPDS Card Number 87-0713)respectively The crystals grew predominantly with a (101)crystallographic orientation This is consistent with previousreferences [28] Figure 3(b) shows the EDAX spectra of Zndeposits on GaNThe EDAX spectra obtained in local pointsof the electrodeposits surface showed that they were mainlycomposed by Zn Gallium and nitrogen were also detecteddue to the GaN substrate The detected oxygen may be

associated with the oxidation of a little part of Zn(0) in thesolution or air

Figure 4(a) shows a family ofCVs of Zndeposited onGaNat different sweep rates With the decrease of sweep rate theZn deposition commences at more positive potential and thepeak current increases Figure 4(b) shows a linear variation ofthe cathodic peak current density as a function of the squareroot of the scan rate (V12) According to Berzins-Delahayequation (3) this linear relation supports the suggestion thatthe growth of zinc metal is a diffusion-controlled process[30]

119894119901

=

06106 (119899119865)32

119862119895

(119877119879)12

11986312

119895

V12 (3)


035 040 045 050 055 060minus33

minus30

minus27

minus24

minus21

Overpotential (V versus AgAgCl)

log jLinear fit of log j

logj

(mA

cmminus2)

Figure 5 Tafel plot for the electrochemical reduction of Zn2+ onGaN electrode The scan rate was 10mV sminus1

Meanwhile the electrochemical behavior of Zn on GaNwas irreversible For electron transfer reaction the cathodictransfer coefficient (120572) can be calculated by the followingequation [31]

10038161003816100381610038161003816119881119901

minus 1198811199012

10038161003816100381610038161003816=

0048

120572

(4)

119881119901

(V) is the peak potential and 1198811199012

(V) is the potential athalf peak height The peak potential depends on the sweeprate and the number of 120572 is 053 at a sweep rate of 10mV sminus1The value of cathodic transfer coefficient is slightly equal toanodic transfer coefficient (1 minus 120572)

It is well known that the electrode kinetics can be simplydescribed by the Butler-Volmer equation

119895 = 1198950

exp [(1 minus 120572) 119911119865119877119879

120578] minus exp [minus120572 119911119865119877119879

120578] (5)

where 119895 (mA cmminus2) presents the current density1198950

(mA cmminus2) is the exchange current density and 120578 (V)is the overpotential For large cathodic overpotentials(|120578| gt 01V) the anodic branch is very small and canbe neglected The resulting Tafel law corresponding toelectrochemical reaction of Zn2+ can then be written as

ln 10038161003816100381610038161198951003816100381610038161003816= ln 1198950

minus 120572

119911119865

119877119879

120578 (6)

Figure 5 illustrates the typical Tafel plot for the elec-trochemical reduction of Zn2+ on GaN electrode It can beseen that a portion of the curve exhibits a linear relationshipin the plot of log 119895 versus potential This indicates that themass transport is the dominant rate-limiting step [28] Inaddition the cathodic exchange current density is estimatedto be sim0132mA cmminus2 which is only slightly lower than thoseon other substrates [7] This is mainly because the number offree electrons in the conduction band of GaN is lower thanmetal

0 20 40 60 80 100minus10

0

10

20

30

40

50

Time (s)

Time (s)00 02 04 06 08 10

minus36minus34minus32minus30minus28minus26minus24minus22minus20

j(m

A cm

minus2)

j(m

A cm

minus2)

(a)

04 05 06 07

08

10

12

14

16

18

20

22

24

26

minusj

(mA

cmminus2)

tminus12 (sminus12)minusj

Linear fit of minusj

(b)

Figure 6 (a) Potentiostatic current transient of Zn deposition onGaN the inset shows an enlargement of the transient curve for thefirst seconds (b) Cottrell plot for the determination of the diffusioncoefficient of Zn2+ species

According to the Cottrell equation diffusion of electroac-tive species in solution could be quantitatively described fromthe diffusion coefficient (119863

119895

cm2 sminus1)

10038161003816100381610038161198951003816100381610038161003816= 119899119865119860119863

12

119895

119862119895

120587minus12

119905minus12

(7)

119895 (A) is the cathodic current density 119899 is the number ofelectrons exchanged and 119860 (cm2) is the effective area of theelectrode119863

119895

represents the diffusion coefficient and119862119895

is theconcentration of Zn2+ Before the occurrence of the limitingcurrent by plotting |119895| = 119891(119905

minus12

) a linear graph would beobtained until the growing diffusion layer has reached itsmaximum width

Figure 6(a) shows potentiostatic current transients ofthe electrodeposition and oxidation process for the Zn onGaN substrate The deposition potential is minus14 V while the


reverse pulse is maintained constant at minus015 V and the pulsetime is 50 s The resulting curves of the transients are atypical response of an electrochemical nucleation and growthprocess The inset shows an enlargement of the transientcurve for the first seconds It is clear that the nucleationstage lasts about 03 s The rapid increase in current at veryshort times indicates the growth of the new phase and theincreasing number of nuclei present on the electrode surfaceAs these grow the coalescence of neighboring diffusionfields with localized spherical symmetry gives rise to acurrent maximum followed by a decaying current related toplanar electrode diffusion It decreases asymptotically untilreaching a constant current value Furthermore the chargesassociated with the reduction and oxidation processes 119876Cand 119876A were obtained by integrating the cathodic andthe anodic branches of the current transients The valuesof 119876C and 119876A were 4195mA and 2983mA respectivelyThat is the efficiency (119876A119876C) of Zn ions reduction onthe GaN electrode was 0689 This further confirmed thatthe electrochemical behavior of Zn on GaN was irreversiblealthough the contribution of hydrogen reduction to the119876C cannot be excluded completely The linear part of theexperimental Cottrell plot can be seen in Figure 6(b) aswell as the corresponding data fit The diffusion coefficient(119863119895

) was evaluated by analyzing the experimental data thatcorresponds to the fall of the direct pulse transients Thediffusion coefficient of 119863

119895

= 333 times 10minus5 cm2 sminus1 was foundfor Zn2+ species This value is comparable to the literatures[4 28 29]

The electrocrystallization process of Zn is limited bydiffusion thus the transients in Figure 5 can be analyzedthrough a 3D growth for an instantaneous nucleation

119895 =

11991111986511986312

119895

12058712

11990512

[1 minus exp (minus1198730

120587119905119870119863119895

)] (8)

or for a progressive type nucleation

119895 =

11991111986511986312

119895

119862119895

12058712

11990512

[1 minus exp(minus2119860119873

0

1205871199052

119870119863119895

3

)] (9)

1198730

(cmminus2) is number density of nucleation active sites119860 (sminus1)is the steady-state nucleation rate active site and 119870 is thenondimensional growth rate constant of a nucleus definedas119870 = (8120587119862

119895

119872120588)12 Table 1 shows the values of nucleation

kinetic parameter Ns for different concentration and poten-tial

The experimental values of 119895119898

and 119905119898

could be obtainedfrom the potentiostatic transients and theoretical maximumvalues can be evaluated by the following equations for theinstantaneous case

119905119898

=

12564

1198730

120587119870119863119895

Ns = 12564

119905119898

120587119870119863119895

119895119898

= 06382119911119865119863119895

119862119895

(1198701198730

)12

(10)

Table 1 The values of nucleation kinetic parameter Ns for eachconcentration and potential

PotentialV 119862119895

(Zn2+)mol cmminus3 Ns(instantaneous)

Ns(progressive)

minus125 1 times 10minus5 078 times 105 126 times 105





for the progressive case

119905119898

= (

46733

1205871198601198730

119870119863119895

)

12

Ns = (A1198730

2119870119863119895

)

12

119895119898

= 0461511991111986511986334

119895

119862119895

(1198701198601198730

)14

(11)

Thus the nondimensional (8) and (9) for the instantaneouscase are

(

119895

119895119898

)

2

=

19542

119905119905119898

1 minus exp [minus12564 ( 119905

119905119898

)]

2

(12)

and for the progressive case are

(

119895

119895119898

)

2

=

12254

119905119905119898

1 minus exp[minus23367 ( 119905

119905119898

)

2

]

2

(13)

Figure 7(a) illustrates current transients for Zn depositiononto GaN electrode within potential range from 125V to14 V Regardless of the electrode potential all the curveshave similar shape and are characterized by sharp increaseof cathodic current at the initial stages of deposition followedby a drop at longer timesThese features of current transientsare relevant to 3D Zn nucleation followed by diffusionlimited growth Figure 7(b) shows the normalized cathodictransients from Figure 7(a) together with the theoreticalcurves for instantaneous and progressive 3D nucleation andgrowth based on (12) and (13) Figure 7(c) shows a series ofdeposition transients for deposition of zinc from the differentconcentration of ZnSO

4

and same potential (minus14 V) Theblack lines of Figures 7(b) and 7(d) are the theoreticalcurves for instantaneous and progressive nucleation Fromthe results in Figure 7(b) in which the solution concentrationof ZnSO

4

is 10mM the first half of the nucleation plot hasgood correlation with the theoretical curve for instantaneousnucleation while the second half of the nucleation plotstransition from progressive to instantaneous nucleation withthe potentials increasing from minus125V (green lines) to minus14 V(red lines) Meanwhile we can know that the mechanismof Zn is different at various concentration from Figure 7(d)and the red green and blue lines are the 5mM 10mMand 20mMThe nucleation plots transition is gradually close


0 5 10 15 20minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2)

minus125V

minus13V

minus14V

(a)

0 1 2 3 4 5

00

02

04

06

08

10

Progressive

Instantaneous

(jj

m)2

ttm

(b)

0 5 10 15 20

minus4

minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2) 5mM

10mM

20mM

(c)

0 1 2 3 4 5

00

02

04

06

08

10

Instantaneous

Progressive

(jj

m)2

ttm

(d)

Figure 7 Potentiostatic current transients for Zn electrodeposition onGaN (a)The concentration of ZnSO4

was 10mMand the potential wasvaried (c)The applied potential was minus14 V while the concentration of ZnSO

4

was varied (b) and (d) are the corresponding nondimensionalplots of (119895119895

119898

)2 versus (119905119905

119898

)

to instantaneous nucleation with increasing Zn2+ concentra-tion

Figures 8(a)ndash8(d) show a family of SEM images of Zndeposits on GaN The applied potential was minus14 V and thedeposition time was varied from 10 20 40 to 80 s It canbe seen that Zn nuclei were formed on GaN electrode andfollowed by a 3D island growth (Volmer-Weber) mechanismbecause of the weak interaction between GaN and Zn Thenuclei density increased and coalescence occurred when thedeposition time was varied from 10 to 80 s

4 Conclusion

The electrodeposition of Zn on 119899-type single-crystalGaN(0001) from a sulphate solution has been studied byelectrochemical techniques and SEM Zn deposition onGaN electrode commenced at a potential of minus112 V without

underpotential deposition and was irreversible and mass-transfer limited The deposition occurred on the conductionband of GaN due to the negative equilibrium potentialMoreover the exchange current density of sim0132mA cmminus2was calculated on the basis of Tafel plot The currenttransient measurements indicated that the depositionprocess accorded with the progressive nucleation

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China (no 21273272) Key Research


1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)

Figure 8 SEM images of Zn deposits on GaN electrode with an applied potential of minus14 VThe deposition time was (a) 10 (b) 20 (c) 40 and(d) 80 s

Program of Jiangsu Province (no BE2015073) and the Chi-nese Academy of Sciences

References

[1] A Gomes and M I Da Silva Pereira ldquoPulsed electrodepositionof Zn in the presence of surfactantsrdquo Electrochimica Acta vol51 no 7 pp 1342ndash1350 2006

[2] P Dıaz-Arista Z I Ortiz H Ruiz R Ortega Y Meas and GTrejo ldquoElectrodeposition and characterization of ZnndashMn alloycoatings obtained from a chloride-based acidic bath containingammonium thiocyanate as an additiverdquo Surface and CoatingsTechnology vol 203 no 9 pp 1167ndash1175 2009

[3] Z F Lodhi J M C MolW J Hamer H A Terryn and J HWDeWit ldquoCathodic inhibition and anomalous electrodepositionof ZnndashCo alloysrdquo Electrochimica Acta vol 52 no 17 pp 5444ndash5452 2007

[4] AGomesA SViana andM IDa Silva Pereira ldquoPotentiostaticand AFMmorphological studies of Zn electrodeposition in thepresence of surfactantsrdquo Journal of the Electrochemical Societyvol 154 no 9 pp D452ndashD461 2007

[5] A Gomes and M I D S Pereira ldquoZn electrodeposition inthe presence of surfactants part I Voltammetric and structuralstudiesrdquo Electrochimica Acta vol 52 no 3 pp 863ndash871 2006

[6] R C M Salles G C G De Oliveira S L Dıaz O E Barciaand O R Mattos ldquoElectrodeposition of Zn in acid sulphatesolutions PH effectsrdquo Electrochimica Acta vol 56 no 23 pp7931ndash7939 2011

[7] G Trejo Y Meas and P Ozil ldquoNucleation and growth ofzinc from chloride concentrated solutionsrdquo Journal of theElectrochemical Society vol 145 no 12 pp 4090ndash4097 1998

[8] J Yu H Yang X Ai and Y Chen ldquoEffects of anions on thezinc electrodeposition onto glassy-carbon electroderdquo RussianJournal of Electrochemistry vol 38 no 3 pp 321ndash325 2002

[9] D S Baik and D J Fray ldquoElectrodeposition of zinc from highacid zinc chloride solutionsrdquo Journal of Applied Electrochem-istry vol 31 no 10 pp 1141ndash1147 2001

[10] E Michelakaki K Valalaki and A G Nassiopoulou ldquoMeso-scopic Ni particles and nanowires by pulsed electrodepositioninto porous Sirdquo Journal of Nanoparticle Research vol 15 no 4article 1499 pp 211ndash214 2013

[11] M L Calegaro M C Santos D W Miwa and S A SMachado ldquoMicrogravimetric and voltammetric study of Znunderpotential deposition on platinum in alkaline mediumrdquoSurface Science vol 579 no 1 pp 58ndash64 2005

[12] H Y Yang X W Guo X B Chen et al ldquoOn the electrodepo-sition of nickel-zinc alloys from a eutectic-based ionic liquidrdquoElectrochimica Acta vol 63 pp 131ndash138 2012

[13] J R I Lee R L OrsquoMalley T J OrsquoConnell A Vollmer andT Rayment ldquoX-ray absorption spectroscopy characterizationof Zn underpotential deposition on Au(1 1 1) from phosphatesupporting electrolyterdquo Electrochimica Acta vol 55 no 28 pp8532ndash8538 2010

[14] R Ozdemir and I H Karahan ldquoElectrodeposition and prop-erties of Zn Cu and Cu1-x Znx thin filmsrdquo Applied SurfaceScience vol 318 pp 314ndash318 2014


[15] D-H Kim W C Lim J-S Park and T-Y Seong ldquoHighlythermally stable PdZnAg ohmic contact to Ga-face p-typeGaNrdquo Journal of Alloys amp Compounds vol 588 no 5 pp 327ndash331 2014

[16] W-S Yum J-W Jeon J-S Sung and T-Y Seong ldquoHighlyreliable AgZnAg ohmic reflector for high-power GaN-basedvertical light-emitting dioderdquo Optics Express vol 20 no 17 pp19194ndash19199 2012

[17] P G Eliseev P Perlin J Furioli P Sartori J Mu andM Osinski ldquoTunneling current and electroluminescence inInGaN ZnSiAlGaNGaN blue light emitting diodesrdquo Journalof Electronic Materials vol 26 no 3 pp 311ndash319 1997

[18] Y Lei J Xu andK Zhu ldquoAGaN-based LEDwith perpendicularstructure fabricated on a ZnO substrate byMOCVDrdquo Journal ofDisplay Technology vol 9 no 5 pp 377ndash381 2013

[19] A Nakajima K Takao and H Ohashi ldquoGaN power transistormodeling for high-speed converter circuit designrdquo IEEE Trans-actions on Electron Devices vol 60 no 2 pp 646ndash652 2013

[20] A V Babichev H Zhang P Lavenus et al ldquoGaN nanowireultraviolet photodetector with a graphene transparent contactrdquoApplied Physics Letters vol 103 no 20 Article ID 201103 2013

[21] M Hirayama Y Ueta T Konishi and S Tsukamoto ldquoNano-clustered Pd catalysts formed on GaN surface for green chem-istryrdquo Journal of Crystal Growth vol 323 no 1 pp 150ndash153 2011

[22] S-Y Chiu H-W Huang T-H Huang et al ldquoComprehensiveinvestigation on planar type of PdndashGaN hydrogen sensorsrdquoInternational Journal of Hydrogen Energy vol 34 no 13 pp5604ndash5615 2009

[23] T Konishi Y Ueta M Hirayama N Nishiwaki and STsukamoto ldquoS-termination effects for the catalytic activities ofPd onGaN(0001) surfacesrdquoApplied Surface Science vol 258 no21 pp 8334ndash8337 2012

[24] Y Zhao F-X Deng L-F Hu Y-Q Liu and G-B PanldquoElectrochemical deposition of copper on single-crystal galliumnitride(0001) electrode nucleation and growth mechanismrdquoElectrochimica Acta vol 130 no 4 pp 537ndash542 2014

[25] Y Li Y Zhao G-B Pan Z-H Liu G-L Xu and K Xu ldquoPrepa-ration of platinum nanoparticles on n-GaN(0001) substrate bymeans of electrodepositionrdquo Electrochimica Acta vol 114 pp352ndash355 2013

[26] R Morita T Narumi and N Kobayashi ldquoSimultaneousmonitoring of hydrogen generation and flat-band potentialby measuring bias dependent photoluminescence of n-typeGaNelectrolyte systemrdquo Japanese Journal of Applied Physicsvol 45 no 4 pp 2525ndash2527 2006

[27] G Oskam J G Long A Natarajan and P C SearsonldquoElectrochemical deposition of metals onto siliconrdquo Journal ofPhysics D Applied Physics vol 31 no 16 pp 1927ndash1949 1998

[28] L E Moron A Mendez F Castaneda et al ldquoElectrodeposi-tion and corrosion behavior of Zn coatings formed using asbrighteners arene additives of different structurerdquo Surface andCoatings Technology vol 205 no 21-22 pp 4985ndash4992 2011

[29] P Dıaz-Arista Y Meas R Ortega and G Trejo ldquoElectrochem-ical and AFM study of Zn electrodeposition in the presence ofbenzylideneacetone in a chloride-based acidic bathrdquo Journal ofApplied Electrochemistry vol 35 no 2 pp 217ndash227 2005

[30] P Delahay and T Berzins ldquoThe Internationale FunkAustellungin Berlin has gotmore electronic innovations that you can pointa remote control at David Phelan Picks the very latest in audio-visual entertainmentrdquo Journal of the American Chemical Societyvol 75 no 10 pp 2486ndash2493 1953

[31] P M Vereecken F V Kerchove and W P Gomes ldquoElectro-chemical behaviour of (100) GaAs IN copper(II)-containingsolutionsrdquo Electrochimica Acta vol 41 no 1 pp 95ndash107 1996

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layer was 5 120583m thick Si-doped and with a carrier concentra-tion of 4 times 1018 cmminus3 Before each experiment the workingelectrode ofGaNwas cleanedwith ultrasonication in acetoneethanol and distilled water successively for 15min The Ptwires (1mm in diameter) were used as counter electrodes

Zinc sulphate (ZnSO4

) boric acid (H3

BO3

) sodiumsulphate (Na

2

SO4

) ethanol and acetone were of analyticalgrade and purchased from Sinopharm Chemical ReagentCo Ltd The electrolyte used in the present study was10mM ZnSO

4

+ 05M H3

BO3

+ 05M Na2

SO4

if it was notmentioned All the solutions were prepared by using Milli-Qwater (gt18MΩ) and all the reagents were used as received

The electrochemical experiments used a standard three-electrode cell arrangement and were undertaken with aCHI 660D potentiostatgalvanostat (Shanghai ChenHua CoLtd) The distance between working and counter electrodeswas about 1 cm The geometric area of GaN in contact withthe electrolyte was 05 cm2 All the potentials were reportedwith respect to a saturated AgAgCl electrode (0197V versusNHE)

The morphology of Zn deposits was investigated byscanning electron microscopy (Hitachi S4800) The X-raydiffraction (XRD) patterns were recorded on a Bruker D8Advance Powder X-Ray Diffractometer at a scanning rate of002∘ sminus1 in the 2120579 range 20 to 80∘ using Cu-Ka radiation(120582 = 15406 A)The energy-dispersiveX-ray analysis (EDAX)was performed on a Quanta 400 FEG SEM at 10 KV

3 Results and Discussion

In principle electrochemical nucleation involves the diffu-sion and charge transfer across the electrolyteelectrode inter-face In comparison with metal electrodes the deposition onsemiconductor electrodes ismore complicatedThis ismainlydue to the unique band structure of semiconductors whichaffects both thermodynamics and kinetics of depositionprocessesThe existence of Zn(Π) in 05MNa

2

SO4

and 05MH3

BO3

solution is generally considered to be Zn2+ due to itsstability The reduction process of Zn2+ can be expressed by

Zn2+ + 2eminus = Zn (1)

The Femi level is close to the conduction band due tothe high doped concentration Figure 1 shows the energyband diagram of the 119899-type GaNelectrolyte interface Itcan be seen that there are two sections For simplicity theredox couple is considered as energy states of the Gerischermodel of energy levels in the right side The midpointbetween the reduction and oxidation states corresponds tothe equilibrium potential 119864OR which is equivalent to aFermi level of a redox system

119864OR = 119864120579

OR + kT ln(119888ox119888red

) (2)

Theband energy ofGaNwas cited from the literature [27]When GaN was in contact with electrolyte the band energywould bend upward More importantly the Fermi energyof semiconductor and solution is equal at the electrostatic

GaN Electrolyte

015

345 9

756

453

150EF EOR

Dred

Dox

NH

EE

(eV

)

Vacu

umE

(eV

)

minus75minus6

minus45minus3

minus15

minus3minus15EC

EV

Figure 1 The energy band diagram for the 119899-type GaNelectrolyteinterface

minus16 minus12 minus08 minus04 00 04minus3

minus2

minus1

0

1

2

3

Potential (V)

OCP

minus095V

minus112V

minus128V

Curr

ent d

ensit

y (m

A cm

minus2)

05M Na2SO4 + 05 H3BO3

10mM ZnSO4 + 05M Na2SO4 + 05 H3BO3

Figure 2 Cyclic voltammograms of GaN electrode at the scan rateof 10mV sminus1

equilibrium condition As a result a space charge layer (SCL)was formed at the interface between semiconductor andsolution which is equivalent to the built-in potential formedat a Schottky junction [27]

Figure 2 presents typical CVs of GaN electrode in 05MH3

BO3

+ 05M Na2

SO4

solution with and without 10mMZnSO

4

at a scan rate of 10mVs The Open Circuit Potential(OCP) was about 018 V In the first cycle the cathodiccurrent started to increasewhen the potential reachedminus112Vindicating the beginning of Zn deposition Moreover anobvious cathodic reduction peak at potential ofminus128V can beobserved As described in the literatures [28 29] the reduc-tion proceeds in a single step (peak at minus128V) associatedwith the reduction of Zn(II) ions to Zn(0) No additionalpeaks are observed before overpotential deposition of Znindicating that no underpotential process occurs This ismainly due to the weak interaction between Zn depositand GaN On the reverse scan the anodic stripping peak isobserved at a potential of minus095V due to the dissolution ofZn In the second cycle the Zn deposition on GaN electrodecommencedmore positive than that of first one because someZn nuclei were still present on the electrode surface


30 40 50 60 70 80 90

Inte

nsity

(au

)

GaN

(100)

(101)

(102)

GaN

(004)(112)(201)

(103)(110)

2120579 (deg)

(a)

05 10 15 20

Inte

nsity

(au

)

Energy (keV)

NO

Zn

Ga

(b)



minus3

minus2

minus1

0

1

2

3

4

5


Curr

ent d

ensit

y (m

A cm

minus2)

5mVs10mVs

20mVs50mVs

(a)

2 3 4 5 6 708

10

12

14

16

18

20

22

minusj

(mA

cmminus2)

12 (mVs)

(b)






119894119901

=

06106 (119899119865)32

119862119895

(119877119879)12

11986312

119895

V12 (3)


035 040 045 050 055 060minus33

minus30

minus27

minus24

minus21



logj

(mA

cmminus2)



10038161003816100381610038161003816119881119901

minus 1198811199012

10038161003816100381610038161003816=

0048

120572

(4)

119881119901




119895 = 1198950

exp [(1 minus 120572) 119911119865119877119879

120578] minus exp [minus120572 119911119865119877119879

120578] (5)



ln 10038161003816100381610038161198951003816100381610038161003816= ln 1198950

minus 120572

119911119865

119877119879

120578 (6)


0 20 40 60 80 100minus10

0

10

20

30

40

50

Time (s)

Time (s)00 02 04 06 08 10


j(m

A cm

minus2)

j(m

A cm

minus2)

(a)

04 05 06 07

08

10

12

14

16

18

20

22

24

26

minusj

(mA

cmminus2)



(b)



119895

cm2 sminus1)

10038161003816100381610038161198951003816100381610038161003816= 119899119865119860119863

12

119895

119862119895

120587minus12

119905minus12

(7)


119895



minus12






119895



119895 =

11991111986511986312

119895

12058712

11990512


120587119905119870119863119895

)] (8)


119895 =

11991111986511986312

119895

119862119895

12058712

11990512


0

1205871199052

119870119863119895

3

)] (9)

1198730


119895




and 119905119898


119905119898

=

12564

1198730

120587119870119863119895

Ns = 12564

119905119898

120587119870119863119895

119895119898

= 06382119911119865119863119895

119862119895

(1198701198730

)12

(10)




Ns(progressive)







119905119898

= (

46733

1205871198601198730

119870119863119895

)

12

Ns = (A1198730

2119870119863119895

)

12

119895119898

= 0461511991111986511986334

119895

119862119895

(1198701198601198730

)14

(11)


(

119895

119895119898

)

2

=

19542

119905119905119898


119905119898

)]

2

(12)


(

119895

119895119898

)

2

=

12254

119905119905119898


119905119898

)

2

]

2

(13)


4


4



0 5 10 15 20minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2)

minus125V

minus13V

minus14V

(a)

0 1 2 3 4 5

00

02

04

06

08

10

Progressive

Instantaneous

(jj

m)2

ttm

(b)

0 5 10 15 20

minus4

minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2) 5mM

10mM

20mM

(c)

0 1 2 3 4 5

00

02

04

06

08

10

Instantaneous

Progressive

(jj

m)2

ttm

(d)



4


119898

)2 versus (119905119905

119898

)



4 Conclusion





Acknowledgments



1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)



References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


30 40 50 60 70 80 90

Inte

nsity

(au

)

GaN

(100)

(101)

(102)

GaN

(004)(112)(201)

(103)(110)

2120579 (deg)

(a)

05 10 15 20

Inte

nsity

(au

)

Energy (keV)

NO

Zn

Ga

(b)



minus3

minus2

minus1

0

1

2

3

4

5


Curr

ent d

ensit

y (m

A cm

minus2)

5mVs10mVs

20mVs50mVs

(a)

2 3 4 5 6 708

10

12

14

16

18

20

22

minusj

(mA

cmminus2)

12 (mVs)

(b)






119894119901

=

06106 (119899119865)32

119862119895

(119877119879)12

11986312

119895

V12 (3)


035 040 045 050 055 060minus33

minus30

minus27

minus24

minus21



logj

(mA

cmminus2)



10038161003816100381610038161003816119881119901

minus 1198811199012

10038161003816100381610038161003816=

0048

120572

(4)

119881119901




119895 = 1198950

exp [(1 minus 120572) 119911119865119877119879

120578] minus exp [minus120572 119911119865119877119879

120578] (5)



ln 10038161003816100381610038161198951003816100381610038161003816= ln 1198950

minus 120572

119911119865

119877119879

120578 (6)


0 20 40 60 80 100minus10

0

10

20

30

40

50

Time (s)

Time (s)00 02 04 06 08 10


j(m

A cm

minus2)

j(m

A cm

minus2)

(a)

04 05 06 07

08

10

12

14

16

18

20

22

24

26

minusj

(mA

cmminus2)



(b)



119895

cm2 sminus1)

10038161003816100381610038161198951003816100381610038161003816= 119899119865119860119863

12

119895

119862119895

120587minus12

119905minus12

(7)


119895



minus12






119895



119895 =

11991111986511986312

119895

12058712

11990512


120587119905119870119863119895

)] (8)


119895 =

11991111986511986312

119895

119862119895

12058712

11990512


0

1205871199052

119870119863119895

3

)] (9)

1198730


119895




and 119905119898


119905119898

=

12564

1198730

120587119870119863119895

Ns = 12564

119905119898

120587119870119863119895

119895119898

= 06382119911119865119863119895

119862119895

(1198701198730

)12

(10)




Ns(progressive)







119905119898

= (

46733

1205871198601198730

119870119863119895

)

12

Ns = (A1198730

2119870119863119895

)

12

119895119898

= 0461511991111986511986334

119895

119862119895

(1198701198601198730

)14

(11)


(

119895

119895119898

)

2

=

19542

119905119905119898


119905119898

)]

2

(12)


(

119895

119895119898

)

2

=

12254

119905119905119898


119905119898

)

2

]

2

(13)


4


4



0 5 10 15 20minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2)

minus125V

minus13V

minus14V

(a)

0 1 2 3 4 5

00

02

04

06

08

10

Progressive

Instantaneous

(jj

m)2

ttm

(b)

0 5 10 15 20

minus4

minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2) 5mM

10mM

20mM

(c)

0 1 2 3 4 5

00

02

04

06

08

10

Instantaneous

Progressive

(jj

m)2

ttm

(d)



4


119898

)2 versus (119905119905

119898

)



4 Conclusion





Acknowledgments



1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)



References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


035 040 045 050 055 060minus33

minus30

minus27

minus24

minus21



logj

(mA

cmminus2)



10038161003816100381610038161003816119881119901

minus 1198811199012

10038161003816100381610038161003816=

0048

120572

(4)

119881119901




119895 = 1198950

exp [(1 minus 120572) 119911119865119877119879

120578] minus exp [minus120572 119911119865119877119879

120578] (5)



ln 10038161003816100381610038161198951003816100381610038161003816= ln 1198950

minus 120572

119911119865

119877119879

120578 (6)


0 20 40 60 80 100minus10

0

10

20

30

40

50

Time (s)

Time (s)00 02 04 06 08 10


j(m

A cm

minus2)

j(m

A cm

minus2)

(a)

04 05 06 07

08

10

12

14

16

18

20

22

24

26

minusj

(mA

cmminus2)



(b)



119895

cm2 sminus1)

10038161003816100381610038161198951003816100381610038161003816= 119899119865119860119863

12

119895

119862119895

120587minus12

119905minus12

(7)


119895



minus12






119895



119895 =

11991111986511986312

119895

12058712

11990512


120587119905119870119863119895

)] (8)


119895 =

11991111986511986312

119895

119862119895

12058712

11990512


0

1205871199052

119870119863119895

3

)] (9)

1198730


119895




and 119905119898


119905119898

=

12564

1198730

120587119870119863119895

Ns = 12564

119905119898

120587119870119863119895

119895119898

= 06382119911119865119863119895

119862119895

(1198701198730

)12

(10)




Ns(progressive)







119905119898

= (

46733

1205871198601198730

119870119863119895

)

12

Ns = (A1198730

2119870119863119895

)

12

119895119898

= 0461511991111986511986334

119895

119862119895

(1198701198601198730

)14

(11)


(

119895

119895119898

)

2

=

19542

119905119905119898


119905119898

)]

2

(12)


(

119895

119895119898

)

2

=

12254

119905119905119898


119905119898

)

2

]

2

(13)


4


4



0 5 10 15 20minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2)

minus125V

minus13V

minus14V

(a)

0 1 2 3 4 5

00

02

04

06

08

10

Progressive

Instantaneous

(jj

m)2

ttm

(b)

0 5 10 15 20

minus4

minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2) 5mM

10mM

20mM

(c)

0 1 2 3 4 5

00

02

04

06

08

10

Instantaneous

Progressive

(jj

m)2

ttm

(d)



4


119898

)2 versus (119905119905

119898

)



4 Conclusion





Acknowledgments



1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)



References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




119895



119895 =

11991111986511986312

119895

12058712

11990512


120587119905119870119863119895

)] (8)


119895 =

11991111986511986312

119895

119862119895

12058712

11990512


0

1205871199052

119870119863119895

3

)] (9)

1198730


119895




and 119905119898


119905119898

=

12564

1198730

120587119870119863119895

Ns = 12564

119905119898

120587119870119863119895

119895119898

= 06382119911119865119863119895

119862119895

(1198701198730

)12

(10)




Ns(progressive)







119905119898

= (

46733

1205871198601198730

119870119863119895

)

12

Ns = (A1198730

2119870119863119895

)

12

119895119898

= 0461511991111986511986334

119895

119862119895

(1198701198601198730

)14

(11)


(

119895

119895119898

)

2

=

19542

119905119905119898


119905119898

)]

2

(12)


(

119895

119895119898

)

2

=

12254

119905119905119898


119905119898

)

2

]

2

(13)


4


4



0 5 10 15 20minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2)

minus125V

minus13V

minus14V

(a)

0 1 2 3 4 5

00

02

04

06

08

10

Progressive

Instantaneous

(jj

m)2

ttm

(b)

0 5 10 15 20

minus4

minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2) 5mM

10mM

20mM

(c)

0 1 2 3 4 5

00

02

04

06

08

10

Instantaneous

Progressive

(jj

m)2

ttm

(d)



4


119898

)2 versus (119905119905

119898

)



4 Conclusion





Acknowledgments



1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)



References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 5 10 15 20minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2)

minus125V

minus13V

minus14V

(a)

0 1 2 3 4 5

00

02

04

06

08

10

Progressive

Instantaneous

(jj

m)2

ttm

(b)

0 5 10 15 20

minus4

minus3

minus2

minus1

0

Time (s)

Curr

ent d

ensit

y (m

A cm

minus2) 5mM

10mM

20mM

(c)

0 1 2 3 4 5

00

02

04

06

08

10

Instantaneous

Progressive

(jj

m)2

ttm

(d)



4


119898

)2 versus (119905119905

119898

)



4 Conclusion





Acknowledgments



1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)



References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


1120583m

(a)

1120583m

(b)

1120583m

(c)

1120583m

(d)



References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article Zn Electrodeposition on Single-Crystal GaN ......Research Article Zn...

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Transcript of Research Article Zn Electrodeposition on Single-Crystal GaN ......Research Article Zn...