Electrical and Optical Properties of AZO Thin Films Fabricated by Using a Facing-target Sputtering System with Hetero-targets

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Electrical and Optical Properties of AZO Thin Films Fabricated by Using a Facing-target Sputtering System with Hetero-targets

Litao Yao ^∗ · Sungbo Seo · Kang Bae · Dongyoung Kim · Myunggyu Choi · Sunyoung Sohn · Hwa-Min Kim · Jong-Jae Kim

Department of Electronics and Display Engineering, Graduate School, Catholic University of Daegu, Gyeongsan 712-702, Korea

(Received 13 December 2013 : revised 27 January 2014 : accepted 6 March 2014)

Al

2

O

3

-doped ZnO (AZO) thin films were fabricated by using a facing-target sputtering (FTS) system with hetero-targets of ZnO and Al

2

O

3

. The electrical and the optical properties of the transparent conductive AZO films were investigated to find the optimal fabrication condition. When the deposition power on the ZnO target was fixed to 100 W, the lowest resistivity of 1.48 × 10

⁻³

Ω·cm was obtained for the AZO film with 2.02 wt.% Al

2

O

3

at a power on the Al

2

O

3

target of 70 W.

The resistivity of the film decreased with increasing of the substrate temperature, and the lowest resistivity, 6.78 × 10

⁻⁴

Ω·cm, was observed at a substrate temperature of 400

^◦

C. This change in the resistivity had a close relation to both the carrier mobility and the carrier concentration in the AZO film. The XRD patterns and the SEM images support the conclusion that the Hall mobility depends on the size of the grains formed in the AZO film.

PACS numbers: 73.61.Tm, 78.66.Jg, 81.15.Cd

Keywords: Transparent conductive oxide (TCO), Facing-target sputtering (FTS), AZO film

T

Ò Þ ù p § U Ù Ã Å 6 ] § ( a' [Â S Ë U ê s0 n É® z º < gX c lc Ü R AZO U c lT c l8 ý

° Ë

Ñ] K ¡X ì Ä· ¹ ÅM X ì Ä ¤V R Ë; c å ¾ Ë X ¢ ì Å

¡P ¡ ^∗ · " k) ç ¹ · 9 ~ ç ¡ · » ò 6 B* å · L |' å ¦ · ) í <` 9 * å · »é s * > · » ø ¶ B<

@

/½ ¨d ¦a Ë :@ / < Æ § @ / < Æ" é ¶ n Û ¼e ¦ Y Us / B N < Æõ , â í ß 712-702

(2013¸ 12 Z 4 13{ 9 ~ Ã Î6 £ §, 2014¸ 1 Z 4 27{ 9 Ã º& ñ : r ~ Ã Î6 £ §, 2014¸ 3 Z 4 6{ 9 > F S X & ñ )

@

/ ¾ Ó ¿ Û ¼( ' a A (FTS: facing-target sputtering) ~ ½ ÓZ O ` ¦ s 6 x # Al

2

O

3

¸i ç ) a ZnO ~ Ã Ì} , 7

£

¤ È Ò" î ¸$ í í ß oÓ ü t AZO ~ Ã Ì} [ þ t` ¦ ] j ¦ s [ þ t _ F g < Æ& h , l & h , ½ ¨ ¸& h : £ ¤$ í 1 p x` ¦ ¸

#

~ Ã Ì} ] j _ þ j& h ¸| ` ¦ Ð % i . ZnO ¿ _ 7 £ x Ã Ì 0 >\ ¦ 100 W Ð ¦& ñ ½ + É â Ä º, Al

2

O

3

¿ _ 7 £ x Ã Ì 0 > 70 W{ 9 M : AZO ~ Ã Ì} _ Al

2

O

3

$ í ì r q H 2.02 wt.% s 9 s M : ~ Ã Ì} _ q $ ½ Ó ° ú כ É r 1.48 × 10

⁻³

Ω·cm Ð þ j è° ú כ` ¦ Ð% i . AZO ~ Ã Ì} _ q $ ½ Ó É r l ó ø Í_ : r ¸ © : r \ " fÂ Ò' 7 £ x < Ê\

& h & h t H X < l ó ø Í : r ¸ 400

^◦

C{ 9 â Ä º\ 6.7 × 10

⁻⁴

Ω·cm & ñ ¸_ © ± ú É r q $ ½ Ó ° ú כ` ¦

Ðs , 400

^◦

C\ ¦ Å # Q" f r 7 £ x H â ¾ Ó` ¦ · p . s Qô Ç q $ ½ Ó_ : £ ¤$ í É r l ó ø Í : r ¸_

o\ É r AZO ~ Ã Ì} _ H o # Q s 1 l x ¸ü < H o # Q_ 0 l x ¸_ oü < x 9 ] X ô Ç ' a > e 6 £ §` ¦ _ p H X

<, : £ ¤ y AZO ~ Ã Ì} ` ¦ + þ A$ í ¦ e H & ñ w n _ ß ¼l \ _ > r H כ s X- r] X J õ SEM % ò © Ü ¼

ÐÂ Ò' S X ÷ &% 3 .

246 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License

(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any

medium, provided the original work is properly cited.

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PACS numbers: 73.61.Tm, 78.66.Jg, 81.15.Cd

Keywords: È Ò" î ¸$ í í ß oÓ ü t (TCO), @ / ¾ Ó ¿ Û ¼( ' a A (FTS), AZO film

I. " e Â ] Ø

Z

} É r È Òõ Ö ¦ õ ± ú É r q $ ½ Ó` ¦ t È Ò" î ¸$ í í ß o Ó

ü t (transparent conductive oxide: TCO) ~ Ã Ì} É r LCD (liquid crystal display), PDP (plasma display panel), OLED (organic light emitting display) 1 p x ¨ î ó ø Í n Û ¼e ¦ Y

Us è \ V , o 6 x ÷ & ¦ e [1–6]. Õ ª× æ, ITO (in- dium tin oxide) H 90% s © _ Z } É r È Òõ Ö ¦ õ Ä ºÃ ºô Ç

¸$ í Ü ¼ Ð K TCO ~ Ã Ì} î r X <" f ¸ © V , o æ ¼s

¦ e . t ë ß , ITO H ´ o u í ß oÓ ü t \ _ ô Ç ç ß | 9 $ í `

§

4 (interstitial pneumonia)_ Ä »µ 1 Ï 0 A+ « >s e H ,

´ o

u _ B © | ¾ Ós & h # Q " é ¶ F s q ø ß é ß & h ¸ t ¦ e

[7–13]. s \ þ j H ITO\ ¦ @ /^ ½ + É Ã º e H TCO Ó ü t

| 9

\ @ /K ´ ú § É r ½ ¨ s À Ò# Qt ¦ e H X <, : £ ¤ y AZO (aluminum-doped zinc oxide) H @ /³ ð& h @ /^ Ó ü t| 9 Ð

"

f 1 l q$ í s \ O ¦ ¸ $ § 4 # ´ ú § É r ' a d s | 9 × æ ÷ & ¦ e

.

&

³F AZO ~ Ã Ì} É r sol-gel ~ ½ ÓZ O s CVD (chemical va- por deposition) ¢ ¸ H Û ¼( ' a A ~ ½ ÓZ O 1 p x Ü ¼ Ð 7 £ x Ã Ì÷ & ¦ e

. : r ½ ¨\ " f H ¿ º > h_ s 7 á x ¿ (hetero target)` ¦ ©

Ã

Ìô Ç @ / ¾ Ó ¿ Û ¼( ' a A (facing target sputtering: FTS)

© u \ ¦ 6 x # AZO ~ Ã Ì} ` ¦ ] j ô Ç . l > r _ # Q 7 £ x

Ã

ÌZ O õ ² ú o , FTS © u H ¿ º ¿ s \ + þ A$ í ÷ & H e ¦

Ý ¼ ? /_ γ- \ ¦ ½ ¨5 Å q > ÷ &# Q ± ú É r Û ¼ · ú § 4 \

"

f ¦x 9 ¸ e ¦ Ý ¼ Ò q t$ í s 0 p x # 7 £ x Ã Ì 5 Å q ¸ Ø

Ô ¦ î ß & ñ & h ~ ½ Ó ` ¦ Ä »t ô Ç © I \ " f ~ Ã Ì} ` ¦ 7 £ x Ã Ì½ + É Ã

º e . ¢ ¸ô Ç l ó ø Íõ e ¦ Ý ¼ s ÷ &# Q e # Q Z } É r

\

-t \ ¦ ° ú H { 9 [ þ t _ l ó ø Í Ø æ[ t` ¦ % 3 ] j½ + É Ã º e H ©

&

h

[ þ t` ¦ ° ú H [14]. : r ½ ¨\ " f H ¿ º > h_ s 7 á x ¿ (hetero target) Al ₂ O ₃ ü < ZnO\ ¦ © Ã Ì ¦ y y _ 0 >\ ¦

or & ¸i ç | ¾ Ó` ¦ ¸] X ½ + É Ã º H FTS © u \ ¦ 6 x # AZO ~ Ã Ì} ` ¦ ] j ¦ s ~ Ã Ì} \ @ /K l & h , F g < Æ& h ,

½

¨ ¸& h : £ ¤$ í 1 p x` ¦ ì r$ 3 # ITO_ @ /^ Ó ü t Ð" f_ 0 p x$ í

`

¦ Ð ¦ ô Ç .

II. ÷ m Ç ] M ö

AZO ~ Ã Ì} ` ¦ 0 Aô Ç Û ¼( ' a A6 x ¿ É r 4N (99.99%) _ Al ₂ O ₃ ü < ZnO ì r ´ ú ` ¦ y y 6 x # ] j % i . ¿

∗

E-mail: [email protected]

Fig. 1. Schematic diagram of the facing target sputtering (FTS) system.

É r 3 inch ] t × ¼\ ¦ s 6 x # · ú Ã Ìõ 1,050 ^◦ C \ " f è$ í õ

&

ñ ` ¦ u ¦, 7 £ x Ã Ì\ 6 x ½ + É slide glass l ó ø Í É r [ j : r, B

jò ø Í` ¦, DI water í H " f Ð y y 10ì rm í6 £ § [ j' l \ ¦ s

6 x # ³ ð s Ó ü t| 9 ` ¦ ] j % i . Fig. 1 É r : r ½ ¨\ s

6 x ) a FTS © u _ ¸d ¸s . AZO ~ Ã Ì} _ 7 £ x Ã Ì ¸|

É r Table 1 \ ] jr ô Ç ü < ° ú . AZO ~ Ã Ì} \ " f Al 2 O ₃ _

¸i ç ª ` ¦ ¸] X l 0 AK ZnO ¿ _ 0 > H 100 W Ð

¦& ñ ¦ Al 2 O 3 ¿ _ 0 >\ ¦ 50 ∼ 90 W t o\ ¦ Å

Ò# Q z ´+ « > % i . ¿ õ ¿ s _ o (d ^{T T} ) H 120 mm, ¿ õ l ó ø Í s _ o (d ^{T S} ) H 90 mm, Ø Ô 4 H _

Ä »| ¾ Ó É r 70 sccm Ü ¼ Ð ¦& ñ % i . ¢ ¸ô Ç 0 >_ o\

É r z ´+ « > õ × æ © ± ú É r q $ ½ Ó` ¦ AZO ~ Ã Ì}

\

@ /K l ó ø Í : r ¸\ ¦ z ´ : r (RT) \ " fÂ Ò' 500 ^◦ C t

or & " f AZO ~ Ã Ì} _ þ j& h ] j ¸| \ @ /K z ´+ « >

% i .

]

j ) a AZO ~ Ã Ì} _ $ í ì r q \ ¦ ¸ l 0 AK Shi- madzu _ & ³p ì r$ 3 l (electron probe microana- lyzer, EPMA)\ ¦ s 6 x % i . \ P % o : r ¸ Z > Ð ] j

)

a AZO ~ Ã Ì} [ þ t _ l & h : £ ¤$ í É r 4 point-probe (MCP- T360, Mitsubishi Chemical Co.) ü < Hall ´ òõ © u (HEM-2000, EGK Co.)\ ¦ 6 x # $ ½ Ó, f . Ë s 1 l x ¸ (Hall mobility) ü < 0 l x ¸ 1 p x` ¦ 8 £ ¤& ñ % i . F g < Æ& h : £ ¤

$ í

É r UV-Vis. Spectrophotometer (Shimadzu)\ ¦ : x K r

F g % ò % i \ " f_ F g È Òõ Û ¼& 7 à Ô! 3 ` ¦ 8 £ ¤& ñ % i Ü ¼ 9 s Ð Â

Ò' F g < Æ& h ½ × ¼ Ì s_ o\ ¦ > í ß % i .

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Table 1. Deposition conditions of the AZO thin films using FTS system.

Parameter Deposition Condition

Targetsize 3 inch

Substrate slide glass Carrier gas Ar, 70 sccm

RF power Al

2

O

3

50 ∼ 90 W

ZnO 100 W

Substrate temperature RT, 100, 200, 300, 400, 500

^◦

C Distance between target

90 mm and substrate (d

T S

)

Distance between

120 mm targets (d

T T

)

Base Pressure 1.0 × 10

⁻⁵

Torr Film thickness 200 nm

ô

Ç¼ # , 7 £ x Ã Ì ) a AZO ~ Ã Ì} _ ¿ ºa H DI Instruments _

³ ð é ß 8 £ ¤& ñ l (surface profiler, α-step)\ ¦ s 6 x # 8

£ ¤& ñ % i . AZO ~ Ã Ì} [ þ t _ ½ ¨ ¸& h : £ ¤$ í [ þ t É r Rigaku _

X- r] X (XRD) J õ Hitachi _ ¦ì r K 0 p x >

~

½ ÓØ ¦ Å Ò & ³p â (high-resolution scanning electron microscope, HR-SEM, S-4800)` ¦ s 6 x # ì r$ 3 % i .

III. + s ÇÊ Ý õ m Í w ² o

Figure 2 H Al 2 O 3 _ 7 £ x Ã Ì 0 >\ É r AZO ~ Ã Ì} _ Al 2 O 3 ¸i ç | ¾ Óõ q $ ½ Ó_ o\ @ /ô Ç Õ ªA á Ôs . AZO

~ Ã

Ì} 7 £ x Ã Ì r , s 7 á x ¿ ` ¦ s 6 x # ZnO ¿ _ 0 >\ ¦ 100 W Ð ¦& ñ ¦ Al 2 O ₃ ¿ _ 0 >\ ¦ 50 ∼ 90 W t

or v " f EPMA\ ¦ s 6 x # 8 £ ¤& ñ ô Ç õ , AZO

~ Ã

Ì} ? /_ Al ² O 3 _ $ í ì r q H y y 1.04, 1.48, 2.02, 2.20, 4.07 wt.% Ð z ¤ . : £ ¤ y , Al ² O 3 _ RF 0 > 70 W 7

£ ¤, Al 2 O 3 _ $ í ì r q 2.02 wt.%{ 9 M : AZO_ q $ ½ Ó É r 1.48 × 10 ⁻³ Ω·cm Ð © ± ú É r ° ú כ` ¦ Ð# Å Ò% 3 . s H Al 2 O 3 _ 7 £ x Ã Ì 0 >\ ¦ 7 £ x r ( \ AZO ~ Ã Ì} ? /\

"

f Al 2 O 3 _ ¸i ç | ¾ Ó É r 7 £ x H X < RF 0 > 50 ∼ 60 W _ â Ä º\ H Al 2 O ₃ _ ¸i ç | ¾ Ós & h # Q Al { 9 Zn\ ¦ Ø

æì r y u ¨ 8 r v t 3 l w ô Ç M :ë H כ Ü ¼ Ð s K ) a . ì ø Í , Al ₂ O ₃ _ 7 £ x Ã Ì 0 > 70 W s © { 9 â Ä º\ H, Al 2 O ₃ _

¸i ç 0 l x ¸ 2.02 wt.% s © { 9 â Ä º AZO_ $ ½ Ó É r r

7 £ x > ) a . s H õ ¸ > ¸i ç ) a Al { 9 s

: r o÷ &t 3 l w ¦ ~ Ã Ì} ? /\ × æ$ í { 9 (neutral particle) + þ

AI Ð > r F < ÊÜ ¼ Ð+ Ä » _ s 1 l x` ¦ ~ ½ ÓK # H o

#

Q s 1 l x ¸\ ¦ y èr v l M :ë H כ Ü ¼ Ð # [15].

Fig. 2. The Al ₂ O ₃ ratios and the resistivity of the AZO films as a function of Al ₂ O ₃ deposition power.

Fig. 3. Optical transmission spectra of the AZO films as a function of wavelength at various substrate tempera- tures.

Figure 3 É r Al 2 O 3 _ $ í ì r q 2.02 wt.% AZO ~ Ã Ì} _

l ó ø Í : r ¸_ o\ É r F g < Æ& h : £ ¤$ í ` ¦ · p Õ ªA á

Ôs . ¸ H AZO ~ Ã Ì} [ þ t É r r F g % ò % i \ " f ¨ î ç H È Òõ Ö

¦ s 85% s © _ Ä ºÃ ºô Ç F g È Òõ : £ ¤$ í ` ¦ ? / 9, l ó ø Í

: r ¸ z ´ : r (room temperature: RT) \ " f 500 ^◦ C & ñ ¸ t

7 £ x > ÷ & F g È Òõ Û ¼& 7 à Ô! 3 _ f ¨ Ã ºé ß (absorption edge) s é ß © A á ¤ Ü ¼ Ð s 1 l x H â ¾ Ó (blue shift)` ¦ ^ ¦ Ã

º e . s Qô Ç f ¨ Ã ºé ß _ s 1 l x É r AZO ~ Ã Ì} [ þ t _ F g < Æ& h {

ç ß (band gap)_ oü < x 9 ] X ô Ç ' a > e .

{ 9

ì ø Í& h Ü ¼ Ð F g È Òõ Ö ¦ (transmittance) T H exp(-αt) \ q

Y V H X < (α H f ¨ Ã º> Ã º, t H ~ Ã Ì} _ ¿ ºa ), f ] X

;s ì ø Í ¸^ \ " f f ¨ Ã º> Ã ºü < F g < Æ& h { ç ß (optical bandgap) E g H 6 £ § õ ° ú É r ' a > Ð ³ ðr ) a .

αhν = A(hν − E g ) ^1/2 (1)

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Fig. 4. Resistivity of the AZO films as a function of the substrate temperatures.

Fig. 5. The carrier concentration and the Hall mobility of the AZO films as a function of the substrate temperature.

#

l " f, A H © Ã º, h H Planck © Ã º, ν H { 9 F g _ 1 l x Ã

ºs . f ] X ;s \ @ /ô Ç f ¨ Ã º> Ã ºü < { 9 F g _ \ -t hν ç ß _ ' a > d (1) ÐÂ Ò' F g < Æ& h { ç ß ` ¦ > í ß ô Ç õ , l

ó ø Í : r ¸\ ¦ z ´ : r \ " f 500 ^◦ C t o\ ¦ × ¦ â Ä º, F g < Æ

&

h { ç ß É r : r ¸ 7 £ x < Ê\ 3.4 eV\ " f 3.5 eV t

ç ß 7 £ x H X <, s H l ó ø Í_ : r ¸ o\ _ K " f H AZO ~ Ã Ì} _ ½ × ¼Ì ss Õ ª t ß ¼> % ò ¾ Ó` ¦ ~ Ã Ît · ú §6 £ §` ¦ _

p ô Ç .

Figure 4 H l ó ø Í : r ¸_ o\ É r AZO ~ Ã Ì} _ q

$

½ Ó` ¦ · p Õ ªA á Ôs . l ó ø Í_ : r ¸ 7 £ x ½ + ÉÃ º2 ¤ q

$ ½ Ó É r " f" fy y è 9 l ó ø Í : r ¸ 400 ^◦ C { 9 M : 6.7

× 10 ⁻⁴ Ω·cm Ð © ± ú É r q $ ½ Ó` ¦ Ðs , 500 ^◦ C s

© s ÷ & r 7 £ x > ) a . Fig. 5 H l ó ø Í : r ¸_

o\ É r H o # Q_ 0 l x ¸ x 9 Hall s 1 l x ¸\ @ /ô Ç 8 £ ¤

&

ñ õ \ ¦ · p כ s . y : r ¸ Z > Ð 7 £ x Ã Ì ) a Ä »o l

Fig. 6. X-ray diffraction spectra of the AZO thin films at various substrate temperatures.

ó

ø Í` ¦ 10 × 10 mm ² _ ß ¼l Ð ¸ ú " f F K ¸F K s ) a f . Ë 8

\

Â Ò Ã Ì # Hall s 1 l x ¸\ ¦ 8 £ ¤& ñ % i Ü ¼ 9, z ´+ « >_ ø @

$ í

S X Ð\ ¦ 0 AK y l ó ø Í { © 5 rm 8 £ ¤& ñ # ¨ î ç H % i Ü ¼ 9 ¸ Ö ¦ É r 5% s Ð z ¤ . Hall s 1 l x ¸ H l ó ø Í : r

¸ 400 ^◦ C \ " f þ j ¦u \ ¦ Ðs H X <, s H Fig. 4 \ " f Ð1 p w s

, s : r ¸\ " f AZO ~ Ã Ì} s © ± ú É r q $ ½ Ó` ¦ Ðs

H · ú ¡_ õ ü < f ] X ' aº H d` ¦ _ p ô Ç . 7 £ ¤, H o # Q 0 l x

¸ H : r ¸ 7 £ x ½ + ÉÃ º2 ¤ Ë ¨ï r y 7 £ x 9, \ P \ -t \ _

K Alõ Zn_ u ¨ 8 s Ö ¸ µ 1 Ïy { 9 # Qè ß כ Ü ¼ Ð Æ Ò& ñ ) a .

q

$ ½ Ó ρ H _ 0 l x ¸ (η), _ s 1 l x ¸ (µ) x 9

(q)_ Y L \ ì ø Íq Y V H ' a > Ð Å Ò# Q .

ρ = 1

ηµq (2)

7 £ ¤, H o # Q 0 l x ¸ü < _ s 1 l x ¸ ° ú כ[ þ t _ Y L s & | 9 Ã º2 ¤ q

$ ½ Ó É r t > ÷ &Ù ¼ Ð, Fig. 5\ " f H o # Q 0 l x ¸ü < H o

ô

Ç¼ # , _ s 1 l x ¸ H & ñ _ ß ¼l \ Å Ò Ð _ > r H X

<, XRD J Ü ¼ ÐÂ Ò' ¸ s z ´` ¦ S X ½ + É Ã º e .

Fig. 6 É r l ó ø Í : r ¸_ o\ É r AZO ~ Ã Ì} [ þ t _ XRD J

_ ì r$ 3 õ \ ¦ · p Õ ªa Ë >s . Õ ªa Ë >\ " f · ú Ã º e 1

p

w s , c-» ¡ ¤ C ¾ Ó$ í ` ¦ t ZnO (002) ~ ½ Ó ¾ ÓÜ ¼ Ð & ñ $ í

H AZO ~ Ã Ì} _ l ó ø Í : r ¸ 400 ^◦ C { 9 M : þ j@ /° ú כ` ¦

· p .

& ñ w n (grain)_ ß ¼l D H Scherrer / B Nd

D = K λ

β cos θ (3)

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Fig. 7. HR-SEM images of the AZO thin films at various substrate temperatures.

`

¦ s 6 x # XRD Û ¼& 7 à Ô! 3 _ ì ø Í; ¤ (full width at half maximum, FWHM) β ÐÂ Ò' Æ Ò& ñ K è q Ã º e . # l " f, K H ¸ ª (shape factor), λ H X- © , θ H Bragg

r] X y ` ¦ _ p H X <, : r z ´+ « >_ â Ä º K = 0.943, λ = 0.15405 nm & h 6 x ÷ &% 3 . d (3)\ _ , l ó ø Í : r

¸ 400 ^◦ C \ " f ] j ) a AZO ~ Ã Ì} _ â Ä º, þ j@ / & ñ w n _ ß

¼l 18.45 nm Ð Æ Ò& ñ ÷ &% 3 . s H 400 ^◦ C \ " f 7 £ x

Ã

Ì ) a AZO ~ Ã Ì} \ " f H, \ P \ -t Ø æì r y / B N/ å LH d Ü ¼ Ð +

#

Q ~ Ã Ì} ? /\ " f _ s 1 l x ¸\ ¦ 7 £ x r & ~ Ã Ì} _ l

&

h

Figure 7 É r AZO ~ Ã Ì} _ SEM ³ ð s p t \ ¦ · p Õ

ªa Ë >s . & ñ w n _ ß ¼l H l ó ø Í : r ¸ 400 ^◦ C \ s Ø Ô l

Å

# Q" f & ñ w n _ ß ¼l H r y è H כ Ü ¼ Ð Ð#

. s H · ú ¡\ " f / å L ô Ç XRD J _ & ñ ß ¼l x 9

>

÷ & 9, 500 ^◦ C \ " f H _ þ t s × ¼ Ä »o l ó ø Í_ + þ A x 9 ¸

%

ô

Ç¼ # , AZO ~ Ã Ì} \ @ /K AFM (atomic force microscope) 8

£ ¤& ñ ` ¦ : x ô Ç ³ ð } 9 l _ RMS (root-mean-square) ° ú כ

É r, l ó ø Í : r ¸ 7 £ x \ 1.454 nm\ " fÂ Ò' 3.446 nm

t Ð & h 7 £ x H z ´` ¦ S X ½ + É Ã º e % 3 .

IV. + s Ç Â ] Ø

: r ½ ¨\ " f H Al 2 O 3 ü < ZnO s 7 á x ¿ (hetero tar- get)` ¦ © Ã Ìô Ç FTS 7 £ x Ã ÌZ O ` ¦ s 6 x # AZO ~ Ã Ì} ? /_ Al ₂ O ₃ $ í ì r q \ ¦ 1.04 wt.% \ " f 4.07 wt.% t ¸] X % i

É r AZO ~ Ã Ì} _ F g < Æ& h , l & h , ½ ¨ ¸& h : £ ¤$ í [ þ t` ¦ ¸

¦ þ j& h ~ Ã Ì} ] j ¸| [ þ t` ¦ Ð % i . Ä »o l ó ø Í0 A

\

$ í } ) a AZO ~ Ã Ì} _ F g È Òõ Ö ¦ É r ª ô Ç : r ¸\ " f $ í }

) a @ /Â Òì r _ ~ Ã Ì} \ " f r F g % ò % i \ " f ¨ î ç H 85% s

r q \ ¦ t m H AZO ~ Ã Ì} ` ¦ l ó ø Í : r ¸ 400 ^◦ C Ð Ä »t

#

] j ½ + É â Ä º, s ~ Ã Ì} É r Ä ºÃ ºô Ç & ñ $ í Ü ¼ Ð K s 1

l

x ¸ 7 £ x x 9 " é ¶ î r1 l x s Ö ¸ µ 1 Ï > { 9 # Q Al Ô ¦í HÓ ü t s Zn o Ð & h ] X y u ¨ 8 ÷ &# Q4 R ² D G 6.7 × 10 ⁻⁴ Ω·cm & ñ

¸_ þ j$ q $ ½ Ó ° ú כ` ¦ t _ ` ¦ · ú Ã º e % 3 . : r ½ ¨\ ¦ :

x K , s 7 á x ¿ ` ¦ 6 x # ~ Ã Ì} ? /_ y Ó ü t| 9 [ þ t _ $ í ì

r q \ @ /ô Ç p [ j ¸] X s 0 p x < Ê` ¦ S X % i Ü ¼ 9, AZO

~ Ã

Ì} É r l > r _ ITO ~ Ã Ì} ` ¦ @ /^ # ¨ î ó ø Ín Û ¼e ¦ Y Us

~ Ã

Ì} + þ A I ª t 6 x È Ò" î F G \ & h 6 x| ¨ c 0 p x$ í s Ø æì r

½

+ É כ Ü ¼ Ð l @ / ) a .

P

c p 8 ý ò k >

: r ½ ¨ H §¹ ¢ ¤ õ < Æl Õ ü t Â Òü < ô Ç² D G ½ ¨F é ß _ t % i + À :

§ 4 ª $ í \ O _ ½ ¨q t " é ¶ \ _ K Ã º' ) a כ e (2012026226).

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Electrical and Optical Properties of AZO Thin Films Fabricated by Using a Facing-target Sputtering System with Hetero-targets

Electrical and Optical Properties of AZO Thin Films Fabricated by Using a Facing-target Sputtering System with Hetero-targets

Litao Yao ∗ · Sungbo Seo · Kang Bae · Dongyoung Kim · Myunggyu Choi · Sunyoung Sohn · Hwa-Min Kim · Jong-Jae Kim

Department of Electronics and Display Engineering, Graduate School, Catholic University of Daegu, Gyeongsan 712-702, Korea

(Received 13 December 2013 : revised 27 January 2014 : accepted 6 March 2014)

Al

O

-doped ZnO (AZO) thin films were fabricated by using a facing-target sputtering (FTS) system with hetero-targets of ZnO and Al

O

. The electrical and the optical properties of the transparent conductive AZO films were investigated to find the optimal fabrication condition. When the deposition power on the ZnO target was fixed to 100 W, the lowest resistivity of 1.48 × 10

Ω·cm was obtained for the AZO film with 2.02 wt.% Al

O

at a power on the Al

O

target of 70 W.

The resistivity of the film decreased with increasing of the substrate temperature, and the lowest resistivity, 6.78 × 10

Ω·cm, was observed at a substrate temperature of 400

C. This change in the resistivity had a close relation to both the carrier mobility and the carrier concentration in the AZO film. The XRD patterns and the SEM images support the conclusion that the Hall mobility depends on the size of the grains formed in the AZO film.

PACS numbers: 73.61.Tm, 78.66.Jg, 81.15.Cd

Keywords: Transparent conductive oxide (TCO), Facing-target sputtering (FTS), AZO film

T

 Ò Þ  ù p § U Ù Ã Å 6 ]  §   ­ ( a' [Â S Ë U ê s0 n É® z º < gX c lc Ü R AZO U c lT c l8 ý

° Ë

Ñ] K ¡X ì Ä· ¹ ÅM X ì Ä  ¤V R Ë; c å ¾ Ë X ¢  ì Å 



 ¡P   ¡ ∗ · " k) ç  ¹ · 9 ~ ç ¡ ·  » ò 6 B* å  · L |' å ¦  · ) í <` 9 * å  ·  »é s * > ·  » ø ¶ B< 

@

/½ ¨d  ¦a Ë :@ / < Æ § @ / < Æ" é ¶    n Û ¼e  ¦ Y Us / B N  < Æõ ,  â í ß  712-702

(2013¸  12 Z 4 13{ 9  ~ Ã Î6 £ §, 2014¸  1 Z 4 27{ 9  Ã º& ñ  : r ~ Ã Î6 £ §, 2014¸  3 Z 4 6{ 9  > F  S X & ñ )

@

/ ¾ Ó  ¿ Û ¼( ' a A (FTS: facing-target sputtering) ~ ½ ÓZ O `  ¦ s 6 x #  Al

O

  ¸i ç  ) a ZnO ~ Ã Ì}  , 7

£

¤ È Ò" î    ¸$ í í ß  oÓ ü t  AZO ~ Ã Ì}  [ þ t`  ¦ ] j    ¦ s [ þ t _  F g  < Æ& h ,   l & h , ½ ¨ ¸& h : £ ¤$ í 1 p x`  ¦  ¸  

#

 ~ Ã Ì}   ] j  _  þ j& h  ¸| `  ¦    Ð % i  . ZnO  ¿ _  7 £ x  Ã Ì 0 >\  ¦ 100 W  Ð  ¦& ñ ½ + É  â Ä º, Al

O





¿ _  7 £ x  Ã Ì 0 > 70 W{ 9  M : AZO ~ Ã Ì}  _  Al

O

$ í ì  r q   H 2.02 wt.% s  9 s M : ~ Ã Ì}  _  q $  ½ Ó ° ú כ É r 1.48 × 10

Ω·cm  Ð þ j è° ú כ`  ¦  Ð% i  . AZO ~ Ã Ì}  _  q $  ½ Ó É r l ó ø Í_   : r  ¸  ©  : r \ " fÂ Ò'  7 £ x  < Ê\ 



  & h & h     t   H X < l ó ø Í  : r  ¸ 400

C{ 9   â Ä º\  6.7 × 10

Ω·cm & ñ  ¸_   ©  ± ú  É r q $  ½ Ó ° ú כ`  ¦



Ðs  , 400

C\  ¦  Å # Q" f  r  7 £ x    H  â  ¾ Ó`  ¦   · p . s  Qô  Ç q $  ½ Ó_  : £ ¤$ í  É r l ó ø Í  : r  ¸_ 



 o\    É r AZO ~ Ã Ì}  _  H o # Q s 1 l x  ¸ü < H o # Q_  0 l x  ¸_    oü < x 9 ] X ô  Ç  ' a >  e  6 £ §`  ¦ _ p    H X

<, : £ ¤ y  AZO ~ Ã Ì}  `  ¦ + þ A$ í  ¦ e    H   & ñ w n _  ß ¼l \  _  > r   H  כ s  X-  r] X  J   õ  SEM % ò  © Ü ¼



ÐÂ Ò'  S X    ÷ &% 3  .

246

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License

(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any

medium, provided the original work is properly cited.

PACS numbers: 73.61.Tm, 78.66.Jg, 81.15.Cd

Keywords: È Ò" î    ¸$ í í ß  oÓ ü t (TCO), @ / ¾ Ó  ¿ Û ¼( ' a A (FTS), AZO film

I. " e Â ] Ø

Z

 } É r È Òõ Ö  ¦ õ  ± ú  É r q $  ½ Ó`  ¦ t   È Ò" î    ¸$ í í ß  o Ó

ü t (transparent conductive oxide: TCO) ~ Ã Ì}   É r LCD (liquid crystal display), PDP (plasma display panel), OLED (organic light emitting display) 1 p x ¨ î ó ø Í n Û ¼e  ¦ Y

Us   è \  V , o   6 x ÷ & ¦ e    [1–6]. Õ ª×  æ, ITO (in- dium tin oxide)  H 90% s  © _  Z  } É r È Òõ Ö  ¦ õ  Ä ºÃ ºô  Ç  



¸$ í Ü ¼ Ð   K  TCO ~ Ã Ì}   î  r X <" f ¸  ©  V , o  æ ¼s 



¦ e   . t ë ß , ITO  H   ´ o u í ß  oÓ ü t \  _ ô  Ç ç ß | 9 $ í ` 

§

4  (interstitial pneumonia)_  Ä »µ 1 Ï 0 A+ « >s  e     H ,  

´ o

u _  B  © | ¾ Ós  & h # Q " é ¶  F    s  q ø ß  é ß & h  ¸ t  ¦ e 

  [7–13]. s \  þ j   H ITO\  ¦ @ /^ ½ + É Ã º e    H TCO Ó ü t

| 9

\  @ /K  ´ ú § É r   ½ ¨ s À Ò# Qt  ¦ e    H X <, : £ ¤ y  AZO (aluminum-doped zinc oxide)  H @ /³ ð& h   @ /^  Ó ü t| 9  Ð

"

f 1 l q$ í s  \ O  ¦    ¸ $ § 4  #  ´ ú § É r  ' a d  s  | 9 ×  æ ÷ & ¦ e 

Litao Yao ^∗ · Sungbo Seo · Kang Bae · Dongyoung Kim · Myunggyu Choi · Sunyoung Sohn · Hwa-Min Kim · Jong-Jae Kim

Ò Þ ù p § U Ù Ã Å 6 ] § ( a' [Â S Ë U ê s0 n É® z º < gX c lc Ü R AZO U c lT c l8 ý

Ñ] K ¡X ì Ä· ¹ ÅM X ì Ä ¤V R Ë; c å ¾ Ë X ¢ ì Å

¡P ¡ ^∗ · " k) ç ¹ · 9 ~ ç ¡ · » ò 6 B* å · L |' å ¦ · ) í <` 9 * å · »é s * > · » ø ¶ B<

/½ ¨d ¦a Ë :@ / < Æ § @ / < Æ" é ¶ n Û ¼e ¦ Y Us / B N < Æõ , â í ß 712-702

(2013¸ 12 Z 4 13{ 9 ~ Ã Î6 £ §, 2014¸ 1 Z 4 27{ 9 Ã º& ñ : r ~ Ã Î6 £ §, 2014¸ 3 Z 4 6{ 9 > F S X & ñ )

/ ¾ Ó ¿ Û ¼( ' a A (FTS: facing-target sputtering) ~ ½ ÓZ O ` ¦ s 6 x # Al

¸i ç ) a ZnO ~ Ã Ì} , 7

¤ È Ò" î ¸$ í í ß oÓ ü t AZO ~ Ã Ì} [ þ t` ¦ ] j ¦ s [ þ t _ F g < Æ& h , l & h , ½ ¨ ¸& h : £ ¤$ í 1 p x` ¦ ¸

~ Ã Ì} ] j _ þ j& h ¸| ` ¦ Ð % i . ZnO ¿ _ 7 £ x Ã Ì 0 >\ ¦ 100 W Ð ¦& ñ ½ + É â Ä º, Al

¿ _ 7 £ x Ã Ì 0 > 70 W{ 9 M : AZO ~ Ã Ì} _ Al

$ í ì r q H 2.02 wt.% s 9 s M : ~ Ã Ì} _ q $ ½ Ó ° ú כ É r 1.48 × 10

Ω·cm Ð þ j è° ú כ` ¦ Ð% i . AZO ~ Ã Ì} _ q $ ½ Ó É r l ó ø Í_ : r ¸ © : r \ " fÂ Ò' 7 £ x < Ê\

& h & h t H X < l ó ø Í : r ¸ 400

C{ 9 â Ä º\ 6.7 × 10

Ω·cm & ñ ¸_ © ± ú É r q $ ½ Ó ° ú כ` ¦

Ðs , 400

C\ ¦ Å # Q" f r 7 £ x H â ¾ Ó` ¦ · p . s Qô Ç q $ ½ Ó_ : £ ¤$ í É r l ó ø Í : r ¸_

o\ É r AZO ~ Ã Ì} _ H o # Q s 1 l x ¸ü < H o # Q_ 0 l x ¸_ oü < x 9 ] X ô Ç ' a > e 6 £ §` ¦ _ p H X

<, : £ ¤ y AZO ~ Ã Ì} ` ¦ + þ A$ í ¦ e H & ñ w n _ ß ¼l \ _ > r H כ s X- r] X J õ SEM % ò © Ü ¼

ÐÂ Ò' S X ÷ &% 3 .

Keywords: È Ò" î ¸$ í í ß oÓ ü t (TCO), @ / ¾ Ó ¿ Û ¼( ' a A (FTS), AZO film

} É r È Òõ Ö ¦ õ ± ú É r q $ ½ Ó` ¦ t È Ò" î ¸$ í í ß o Ó

ü t (transparent conductive oxide: TCO) ~ Ã Ì} É r LCD (liquid crystal display), PDP (plasma display panel), OLED (organic light emitting display) 1 p x ¨ î ó ø Í n Û ¼e ¦ Y

Us è \ V , o 6 x ÷ & ¦ e [1–6]. Õ ª× æ, ITO (in- dium tin oxide) H 90% s © _ Z } É r È Òõ Ö ¦ õ Ä ºÃ ºô Ç

¸$ í Ü ¼ Ð K TCO ~ Ã Ì} î r X <" f ¸ © V , o æ ¼s

¦ e . t ë ß , ITO H ´ o u í ß oÓ ü t \ _ ô Ç ç ß | 9 $ í `

4 (interstitial pneumonia)_ Ä »µ 1 Ï 0 A+ « >s e H ,

u _ B © | ¾ Ós & h # Q " é ¶ F s q ø ß é ß & h ¸ t ¦ e

[7–13]. s \ þ j H ITO\ ¦ @ /^ ½ + É Ã º e H TCO Ó ü t

\ @ /K ´ ú § É r ½ ¨ s À Ò# Qt ¦ e H X <, : £ ¤ y AZO (aluminum-doped zinc oxide) H @ /³ ð& h @ /^ Ó ü t| 9 Ð

f 1 l q$ í s \ O ¦ ¸ $ § 4 # ´ ú § É r ' a d s | 9 × æ ÷ & ¦ e

.

³F AZO ~ Ã Ì} É r sol-gel ~ ½ ÓZ O s CVD (chemical va- por deposition) ¢ ¸ H Û ¼( ' a A ~ ½ ÓZ O 1 p x Ü ¼ Ð 7 £ x Ã Ì÷ & ¦ e

. : r ½ ¨\ " f H ¿ º > h_ s 7 á x ¿ (hetero target)` ¦ ©

Ã

Ìô Ç @ / ¾ Ó ¿ Û ¼( ' a A (facing target sputtering: FTS)

© u \ ¦ 6 x # AZO ~ Ã Ì} ` ¦ ] j ô Ç . l > r _ # Q 7 £ x

Ã

ÌZ O õ ² ú o , FTS © u H ¿ º ¿ s \ + þ A$ í ÷ & H e ¦

Ý ¼ ? /_ γ- \ ¦ ½ ¨5 Å q > ÷ &# Q ± ú É r Û ¼ · ú § 4 \

f ¦x 9 ¸ e ¦ Ý ¼ Ò q t$ í s 0 p x # 7 £ x Ã Ì 5 Å q ¸ Ø

Ô ¦ î ß & ñ & h ~ ½ Ó ` ¦ Ä »t ô Ç © I \ " f ~ Ã Ì} ` ¦ 7 £ x Ã Ì½ + É Ã

º e . ¢ ¸ô Ç l ó ø Íõ e ¦ Ý ¼ s ÷ &# Q e # Q Z } É r

-t \ ¦ ° ú H { 9 [ þ t _ l ó ø Í Ø æ[ t` ¦ % 3 ] j½ + É Ã º e H ©

[ þ t` ¦ ° ú H [14]. : r ½ ¨\ " f H ¿ º > h_ s 7 á x ¿ (hetero target) Al ₂ O ₃ ü < ZnO\ ¦ © Ã Ì ¦ y y _ 0 >\ ¦

or & ¸i ç | ¾ Ó` ¦ ¸] X ½ + É Ã º H FTS © u \ ¦ 6 x # AZO ~ Ã Ì} ` ¦ ] j ¦ s ~ Ã Ì} \ @ /K l & h , F g < Æ& h ,

¨ ¸& h : £ ¤$ í 1 p x` ¦ ì r$ 3 # ITO_ @ /^ Ó ü t Ð" f_ 0 p x$ í

¦ Ð ¦ ô Ç .

AZO ~ Ã Ì} ` ¦ 0 Aô Ç Û ¼( ' a A6 x ¿ É r 4N (99.99%) _ Al ₂ O ₃ ü < ZnO ì r ´ ú ` ¦ y y 6 x # ] j % i . ¿

É r 3 inch ] t × ¼\ ¦ s 6 x # · ú Ã Ìõ 1,050 ^◦ C \ " f è$ í õ

ñ ` ¦ u ¦, 7 £ x Ã Ì\ 6 x ½ + É slide glass l ó ø Í É r [ j : r, B

jò ø Í` ¦, DI water í H " f Ð y y 10ì rm í6 £ § [ j' l \ ¦ s

6 x # ³ ð s Ó ü t| 9 ` ¦ ] j % i . Fig. 1 É r : r ½ ¨\ s

6 x ) a FTS © u _ ¸d ¸s . AZO ~ Ã Ì} _ 7 £ x Ã Ì ¸|

É r Table 1 \ ] jr ô Ç ü < ° ú . AZO ~ Ã Ì} \ " f Al 2 O ₃ _

¸i ç ª ` ¦ ¸] X l 0 AK ZnO ¿ _ 0 > H 100 W Ð

¦& ñ ¦ Al 2 O 3 ¿ _ 0 >\ ¦ 50 ∼ 90 W t o\ ¦ Å

Ò# Q z ´+ « > % i . ¿ õ ¿ s _ o (d ^{T T} ) H 120 mm, ¿ õ l ó ø Í s _ o (d ^{T S} ) H 90 mm, Ø Ô 4 H _

Ä »| ¾ Ó É r 70 sccm Ü ¼ Ð ¦& ñ % i . ¢ ¸ô Ç 0 >_ o\

É r z ´+ « > õ × æ © ± ú É r q $ ½ Ó` ¦ AZO ~ Ã Ì}

@ /K l ó ø Í : r ¸\ ¦ z ´ : r (RT) \ " fÂ Ò' 500 ^◦ C t

or & " f AZO ~ Ã Ì} _ þ j& h ] j ¸| \ @ /K z ´+ « >

% i .

j ) a AZO ~ Ã Ì} _ $ í ì r q \ ¦ ¸ l 0 AK Shi- madzu _ & ³p ì r$ 3 l (electron probe microana- lyzer, EPMA)\ ¦ s 6 x % i . \ P % o : r ¸ Z > Ð ] j

)

É r UV-Vis. Spectrophotometer (Shimadzu)\ ¦ : x K r

F g % ò % i \ " f_ F g È Òõ Û ¼& 7 à Ô! 3 ` ¦ 8 £ ¤& ñ % i Ü ¼ 9 s Ð Â

Ò' F g < Æ& h ½ × ¼ Ì s_ o\ ¦ > í ß % i .