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Ss Ms 42(2)(2013): 187192

Fbcto d Tspot Pfomc Cctto of Cmc-Dopd

T-bc Jucto Gp Dvc

(Fabrkas da Cr Prstas Agkta Prat Gra Brstrktr Tga Cabag yag Ddp Scara Kma)

Shaharin FaDzli aBD rahMan*, Seiya KaSai & aBDul ManaF haShiM

ABSTRACT

A graphene-based three-branch nanojunction (TBJ) device having nanowire width of 200 nm was successfully fabricated.

The layer number of graphene prepared by mechanical exfoliation was determined using a simple optical contrast method

which showed good agreement with theoretical value. n-type doping by Polyethylene imines (PEI) was done to control

the position of Dirac point. Baking andPEIdoping was found to decrease contact resistance and increase the carrier

mobility. The chemically-dopedTBJgraphene showed carrier mobility of 20000 cm2/Vs, which gave related mean free

path of 175 nm.

Keywords: Chemical doping; graphene; three-branch junction device

ABSTRAK

Peranti berstruktur tiga cabang (TBJ) daripada gran yang mempunyai cabang selebar 200 nm telah berjaya difabrikasi.

Bilangan lapisan gran yang telah disediakanmenggunakan kaedah pengelupasan secara mekanikal, telah ditentukan

menggunakan kaedah kontras optik yang mudah dankeputusan uji kaji selari dengan nilai teori. Pendopan kepada

jenis-n telah dibuat menggunakan polyethylene imines (PEI) untuk mengawal kedudukan titik Dirac. Pemanasan dan

pendopan oleh PEIdidapati telah merendahkan rintangan sentuhan logam dan menaikkan mobiliti pembawa. Gran

TBJyang didop secara kimia telah menunjukkan mobiliti pembawa setinggi 20000 cm2/Vs, menjadikan purata laluan

bebas sejauh 175 nm.

Kata kunci: Gran; pendadahan secara kimia; peranti berstruktur tiga cabang

inTRoDuCTion

T-bc jucto (TBJ), smp odvc cossts

of t ow bcs (Fgu 1), s sow to xbt

uqu o votg tsf cctstc v t

oom tmptu (Xu 2001). Sv studs ssoctd

t obsvd bvou wt bstc tspot of cs

og t put bcs of t dvc d pdctd g

fquc opto of TBJ dvc (i & Sobowsk

2010; Mtos t . 2003). atoug t mcsm of

th arty rmas car (Kasa t a. 2008),

xpmt woks wc m focusd o iii-V

smcoducto-bsd g-cto-mobt-tssto

(heMT) stuctu sowd t TBJ pott fo vous

dvc ppctos (abd rm t . 2009; Soubko

t . 2002; Woscc t . 2002). rct, TBJ

stuctu o gp s b studd d dmosttd

(Gockt t . 2011; Jcobs t . 2010). T wok ws

motvtd b t supo c mobt of gp,

wc b bstc tspot v t mco-sc

(Moov t . 2011). Futmo, t gt-cotod

mbpo tspot gp s xpctd to cs

t fuctot of t TBJ dvc (Jcobs t . 2010).

howv, fut totc d xpmt stud sdd to udstd fudmt opto of t TBJ

dvc fo pctc ppctos.

i ts pp, w pst t fbcto pocss

of gp-bsd TBJ d vut t bsc tspot

popts of t fbctd dvc. Fo gp

mbr dtcat, w adptd a smp ptca ctrast

mtod usg tpc optc mcoscop. T fbctd

dvc ws t ttd b pot ms (Pei) to

coto t Dc pot (VDc) d c t cmobt. Fo to of TBJ opto t bstc

gm, vuto o tspot popts suc s

iput 1 (V) iput 2 (V

)

Output 1 (Vout

)ow jucto

V

Vout

FiGuRe 1. Scmtc dgm d votg

tsf cuv ofTBJ dvc

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188

cotct sstc, c mobt d m f pt s

mpott.

DeviCe FABRiCATion

Fgu 2() sows optc mcoscop mg of gp

ak fr fabrcat f th TBJ dvc. i ts stud, tgraph aks wr prpard by th mcrmchaca

xfoto of t tu ks gpt. T xfotd

gp w tsfd oto 300 m-tck SO2

dpostd o p-S substt. T umb of t

prpard graph aks was dtd sg a ptca

ctrast mthd (Bak t a. 2007; n t a. 2007; n t

. 2011). Fom t RGB mg of t gp tk b t

optc mcoscop, t tst of t g c ws

xtctd d usd to ccut g coo cotst vu,

C=1-(Rwg

/Rwog

), wRwg

dRwog

w t g c

tsts of gp sufc d b SO2

sufc,

spctv. as sow Fgu 2(b), t g cooctrast f th ak was 0.05. Basd th thrtca

vu computd fom Fss w mod, t gp

ak was xpctd t b a sg ayr graph. i rdr

to vdt t suts, g coo cotst fo vous

graph aks wr cacatd ad pttd Fgr 3(a).

Fo fut ss o t cotst dstbuto, stogm

of t g coo cotst s pottd Fgu 3(b). Sv

pks cospodg to dfft umb coud b

obsvd Fgu 3(b). T, vg vu d stdd

dvto of c pk ws xtctd d compd wt

totc vus (dsd s) Fgu 3(c). it s

otd tt t xpmt cotst vus sowd 10%

ctat, whch s attrbtd t th ctat f So2

tckss. T xtctd pk vus gd w wt t

thrtca as crmg th adty f th mthd

usd ts stud. Fom Fgu 3, t mmum cotst

vu, wc cospodg to sg gp, ws

0.0480.009. as t ccutd cotst fo smp

Fgu 2 ws wt t g fo sg , t smp

coud b dtmd s sg .

nxt, omc cotcts d TBJ stuctu w fomd o

t gp Fgu 2(). Fgu 4() sows scmtc

ustto of t gp-bsd TBJ dvc. Omc

cotcts w fomd b stdd mt dposto d

ft-off pocss usg cto bm (eB) thgraphy. 35

m-tck PtPd o ws dpostd usg psm sputtg.

a optc mg ft PtPd dposto d ft-off pocss

s sow Fgu 4(b). as xpctd fo t f-mt

mt k gp, good omc cctstcs coud

b s obtd wtout post g pocss. Fomcut-votg (I-V) cctstcs of two-tm

gp dvcs wt PtPd cotcts, t tot sstc

btw th ctacts ard frm sra k t 10 k.

T, w fbctd t TBJ stuctu b eB togp

d oxg psm tcg usg ctv-o tcg

(rie) sstm. T tcg ws do fo 10 s wt O2

w

t, pssu d rF pow of 20 sccm, 20 P d 100

W, spctv. Fgu 4(c) sows scg cto

mcoscop (SeM) t fbctd TBJ stuctu. T TBJ

stuctu vg bc wdt of 200 m d gt of

800 m ws succssfu fomd.

FiGuRe 2. () Optc mg of moo gp d (b) t

ccutd cotst mg

() (b) (c)

FiGuRe 3. (a) Masrd gr cha ctrast as f ptca mcrscp mags fr a mbr f graph aks,

(b) ts stogm d (c) compso btw xpmt d to, n s t umb of t gp

Smp umb Cotst [.u] l umb

Contrast

Frequency

Contrast

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aft t compto of t fbctd pocss, -tp

dopg b Pei ws pfomd (Fm t . 2008). it

ws foud tt most of t s-fbctd dvcs, t

ambpar ctrc d ffct cd t b bsrd as

VDc

w bod t mt of ou msumt stup.

Ts ws du to t p-tp dopg b dsobd wt- d

oxg-mocu o t gp d SO2sufc (n t

a. 2010). By bakg th dc at 200C fr 1 h fwd

b mmsg to Pei fo o d, t cotmtos

d dsobd mocus coud b ducd d t VDc

coud b djustd to o votg. hvg VDc

o

gt votg ows us to vut t popts of o

d cto tspot d so go VDc

. Bsds

t VDc

sftg, w so obsvd t c mobt

mpovmt ft t dopg pocss. T dts w b

dscussd t xt scto.

eleCTriCal CharaCTerizaTiOn

Fgr 5 shws th masrd trasfr charactrstcs

og c bc bfo d ft t dopg pocss.

i ts msumt, votg, VBG

, ws ppd to t S

substt s bck gt votg w votg d cut

ws ppd d msud, spctv, btw two

bcs s sow Fgu 4(). T s-fbctd dvc

sowd opto s p-tp tssto d VDc

coud ot

b crmd bfr th bakg ad dpg prcss. Aftr

t dopg pocss, VDc

sftd to 4.9 V d t tsf

cuvs bcm stp. Ts dctd t mpovmt

of c mobt. nxt, stmto d ccuto of

cotct sstc, c mobt () d m f pt

(l) ws do fo gt d ft bcs ofTBJ dvc. i

t tpc opto ofTBJ dvc, tspot popts ofrght ad ft brachs pay sgcat r t dtrm

t output votg ct bc.

Fst, cotct sstc t gt d ft bcs ws

stmtd fom t msud tsf cctstcs of

two-tm dvc. it s potd tt t g VBG

gm,

t msud cut stuts t ct vu wc s

dtmd b t cotct sstc. T obtd sdu

sstc t ts gm cospodd wt t cotct

sstc d gd wt t sut fom tsf gt

mtod msumt (Vugop t . 2010). i Fgu

5(a), crrt ag rght ad ft brachs satratd at 16

A. Basd th cacatd rsda rsstac a, th

sum of cotct sstc gt d ft bcs (rC)

was 6.25 k. Th fabrcatd dc shwd typca ctact

sstc vu fo gp/mt tfc. Tpc

gp/mt tfc s potd to sow tv

g sstc du to ow dst of stt gp.

aft t dopg pocss, c cut stuto coud

ot b obsvd. To stmt t sdu sstc, tot

sstc (Rtot

=Vrl

/Irl

) s fucto of 1/(VBG

-VDc

)

was pttd Fgr 6.Irl

s t msud cut og

t c w Vrl

ws ppd btw gt d

FiGuRe 4. () Scmtc ustto ofTBJ dvc, (b) optc mg ft dposto of PtPd cotct

d (c) SeM mg of t fbctd TBJ stuctu

FiGuRe 5. Trasfr charactrstcs ag ach brach (a) bfr ad (b) aftr bakg ad dpg prcss

Branchcurrent(A)

Branchcurrent(A)

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190

sut bfo bkg d dopg pocss s t posto

ofVDc

cd t b crmd frm th masrmt.

T, t ffctv mobt (ff

) ws ccutd b

eff

= (2)

wL d Ws dstc btw gt d ft bcs

d c wdt, spctv. Fgu 7(b) sows t

tosp btw ff

d nd

. Fo coct stmto

offf

, mobt vu t g nd

ws cosdd. at ow

c coctto, t c ducd b mput

cot b gctd, d ts m ffct t stmtd

mobt. Fom Fgu 7(b),ff

of o d cto w

stmtd s 21000 cm2/Vs d 20000 cm2/Vs, spctv.

o th thr had, th d ffct mbty cd b

ccutd fom t tscoductc t gm

of tsf cctstcs (rumtsv t . 2010).

FE

= (3)

gm0

s t t tscoductc gv b

gm0

= (4)

Fgu 8(b) sows tscoductc of dvc ft

bkg d dopg pocss s fucto ofVBG. Basdo t bov qutos, t

Fefo o d cto

w 22100 cm2/Vs d 22700 cm-2/Vs, spctv.

T ccutd Fe

dd ot dff fom t vus offf

crmg th adty f th as. W as td hr

tt t obtd mobt vus coud b cosdd

v g fo gp o SO2

sufc, w t tpc

vu s bow t 10000 cm2/Vs. T bkg d dopg

pocss sm to cs t mobt of t fbctd

dvc bov t tpc vu.

T mpovmt of t mobt coud b xpd

b t ducto of cgd mput dst (n) ft

1/(VBG

VDc

) (1/V)

Rtotal

(k)

FiGuRe 6.Rtot

s fucto of 1/(VBG

-VDc

)

ft bcs. extpotg t cuv to 0 gv sdu

rsstac, whch wr 5.2 k ad 4.0 k fr p- ad -typ

coducto, spctv. it ws foud tt t cotct

sstc sgt dcsd ft t bkg pocss. Ts

ffct f th bakg prcss was as crmd wth thr

smps.

nxt, w ccutd t o d cto mobt

frm masrmt rsts Fgr 5. i gra, fr a

tssto dvc, t two tps of mobt; ffctv

mobt (ff

) ad d ffct mbty (Fe

). T ffctv

mobt s ccutd fom t c coductc o

rsstac, wh th d ffct mbty s xtractd frm

t tscoductc (gm) of t dvc. i ts stud,

bot mobts w ccutd d compd fo t

compso. Fst, od to ccut mobt, ffctvc sstc (R

ff) ws ccutd (rumtsv t .

2010).

Reff

= (1)

0

s t coductvt t VDc

. Fgu 7() sowsRff

s

fucto ofVBG

-ducd c coctto (nd

). T

c coctto s gv b nd

=(Cg(V

BG-V

Dc))/,

w Cg

s gt cpctc of 300 m-tck SO2

d

e s mt cg. h, w dd ot cosd t

d ( 10

12

cm

-2

)

Reff

(k)

d ( 1012

cm

-2

)

eff

(cm

2/Vs)

FiGuRe 7. ()Rff

s fucto ofd

d (b)ff

s fucto d

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191

t dopg pocss (hwg t . 2007).T mobt of

moo gp s kow to vs popoto

to n(Shafq t a. 2007). Wh dpat s addd t

c gp c, n css d t mobtsoud dcs. howv, f t dopt s ddd oto

c vg umb of mputs, t ddd dopt

w fucto s compsto tt dcss t umb

of mputs. Tus, c t mobt ft t dopg

pocss. Ts pomo ws so obsvd sv

xpmt studs bfo (Scd t . 2007). i od

to ccut t cg ofn, w dd oug stmto of

Fe

wtout tkgRC

d 0to ccout.

FEapprox

= (5)

T tscoductc s fucto ofVBG

s sow

Fgu 8().Feppox

fo o ws foud to b csd

fom 430 to 8400 cm2/Vs ft t bkg pocss. T

mobt mpovmt cospodd wt t ducto

f mprty dsty t 0.05 tms f that bfr th

dopg pocss. T mput dst ft Pei dopg ws

cacatd frm th btad mbty (Shafq t a.

2007). Fom t mobt of 20000 cm2/Vs, t mput

dst ws ccutd to b 2.4 1019 cm-2. atoug

t dopg pocss sowd pomsg ffct fo mobt

cmt, fut sstmtc stud ds to b do

to coto ts ffct.

F, w stmtd t m f pt of c ou fbctd dvc. Fo m f pt ccuto,

mobt () f 15000 cm2/Vs d c coctto (n)

of 1 1012 cm-2 ws cosdd. T m f pt (l) s

gv b:

l =

(6)

h s Pck costt. T ccuto gv m f pt

f 175 m. Th cha gth f th fabrcatd dc

was 5.7 tms gr tha th cacatd ma fr path,

dctg tt cs coutd sv scttg ogth cha. Basd th rst, t ca b ccdd that

t fbctd TBJ dvc opts t dffus gm t oom

tmptu. Dcsg t dvc dmso bow t

150 m w aw dc prat at bastc rgm.

ConCluSion

Fbcto pocsss of t gp-bsd TBJ w

pstd. Gp fks ppd b mcc

xfoto mtod w cctd b t optc

cotst mtod. Gp-bsd TBJ dvc wt

ow wdt of 200 m ws succssfu fbctd b

eB togp d oxg psm tcg. T bkg

pocss ws foud to mpov t omc cotct, w

t Pei dopg coud b usd to coto VDc

d c

t c mobt. aft t bkg d dopg pocss,

t fbctd dvc sowd c mobt of 20000

cm2/vs whch ga a ratd ma fr path ard 175

m. Basd ths a, th fabrcatd dc s xpctd

to opt t dffusv gm t t bstc gm.

Dcrasg th dc dms bw tha 150 m

soud b bstc opto t oom tmptu.

ACKnoWleDGeMenTS

W tk Pof. Tks Fuku d Pof. Tmotsu

hsum fo t suppots. S.F.a. rm tks

urst Tkg Maaysa ad th Maaysa Mstry

of hg educto (MOhe) fo t scosp dug

t P.D couss. Ts wok s pt suppotd b FrGS

d erGS gts, Ms Mst of hg educto(MOhe) ad Grats--Ad fr Sctc Rsarch, Japa

Soct fo t Pomoto of Scc (JSPS).

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S Fd abd rm*

Fcut of ectc egg

urst Tkg Maaysa

81310 uTM Skud, Joo

Ms

Sya Kasa

Gdut Scoo of ifomto Scc d Tcoog

d rsc Ct fo itgtd Qutum ectocs

Hkkad ursty

n14, W9, Sappr 060-0814

Jp

abdu Mf hsm

Ms-Jp itto isttut of Tcoog (MJiiT)urst Tkg Maaysa itrata Camps

J Smk

54100 Kaa lmpr

Ms

*Cospodg uto; m: sfd@fk.utm.m

rcvd: 7 Ju 2012

accptd: 21 M 2012