Synchrotron radiation XAFS studies of transition metal oxide thin films prepared

by reactive magnetron sputtering

Juris PurānsInstitute of Solid State Physics University of Latvia

Internet: http://www.cfi.lu.lv/exafs/E-mail: purans@cfi.lu.lv http://www1.cfi.lu.lv/teor/ERAF/

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Transparent Conductive Oxides

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Transparent Conductive Oxides (TCO)

From 1980 =>n-type TCOs, with good optical and electrical properties

http://www.iesl.forth.gr/conferences/tco2006/index.aspx RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

T. Minami, Semicond. Sci. Technol. 20(2005) S35-S44.

Transparent Conductive Oxides

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Time variable (”chromogenic”) window coatings

PhotochromicThermochromicElectrochromicGasochromicUV irradiationTemperatureElectric voltage or chargeReducing/oxidizing gas

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Operating the Electrochromic Element

The ECE can be colored by applying negative potential (-2.4 < U < 0 V)to the working electrode (WE) for a time t < 5 sec.

W6+O3 +e- + H+ => HW5+O3

The ECE can be bleached by applying positive potential (0 < U < +1.5 V)to the working electrode (WE) for a time t < 5 sec.

W6+O3 +e- + H+ <= HW5+O3RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Why zinc oxide ?

• Resource availability• Low cost material• Non-toxicity• High thermal/chemical stability• Electrical resistivity tailored [1010-10-4Ωcm]• High transmittance in the VIS-IR• Lithography compatible ZnO

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Why Ga as dopant?

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Presently HF magnetron sputtering is the background of the technology, but it is underproductive and quite expensive in comparison with DCand MF magnetron sputtering

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

XRD Results RT, Cu anode

30 40 50 60 70

Si

Zn

TEC5/Si

(004

)(2

01)

(112

)(2

00)

(103

)(110

)

(102

)

(101

)

(002

)(1

00)

TEC2/Si

TEC1/Si

c-ZnO

Inte

nsi

ty (

cps)

2 (degree)

30 40 50 60 70

338

7%Cd 480HT2_30s

347HT_30s

346HT_30s

341HT

341HT2(from met-Zn)

Inte

nsi

ty (

cps)

2 (degree)RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

ZnO samples prepared in ISSP (EXAFS Lab.) ZnO samples prepared in ISSP (EXAFS Lab.) morphologymorphology

1.0µm

ZnO/Si produced by magnetron sputtering in argon

followed by oxidation in air at 800ºC

1.0µm

ZnO/Si produced by magnetron sputtering in Ar-O2

APCVD ZnO/Si sample(image size: 890 660 µm)

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

DC magnetron deposition of Zn-based TCO-s: process control by plasma optical emission spectroscopy

R.Kalendarev, K.Vilnis, A.Ecis, M.Zubkins, A.Azens, J.PuransInstitute of Solid State Physics, University of Latvia, Riga, Latvia

The scope: the usefulness of plasma Optical Emission Spectroscopy (OES) for the sputtering process tuning has been investigated with the aim to ensure the process stability and reproducibility, and the quality of ZnO:Al films in terms of [minimized] electrical resistivity and [maximized] optical transmittance

400 500 600 700 800 900 10000

5000

10000

760 770 780 7900

500

1000

1500

2000

Ar

(763

.51n

m)

Zn

(481

.05n

m)

Inte

nsity

(co

unts

)

Inte

nsity

(co

unts

)

Wavelength (nm)

Wavelength (nm)

O (

777.

19,

777.

41,

777.

53 n

m)

Optical emission spectrum upon sputtering of a ZnAl target in an atmosphere of Argon and Oxygen RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

Selected Zinc, Argon and Oxygen optical emission line intensities during the process conditioning and film deposition

0 5 10 15 20 25 300

2000

4000

6000

8000

10000

12000

O (777.19, 777.41, 777.53nm)

Ar (763.51nm)

Inte

nsi

ty (

cou

nts

)

Time (min)

conditioning deposition

Zn (481.05nm)

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

8 10 12 14 160,000

0,002

0,004

0,006

0,008

0,010

Re

sist

ivity

, oh

m*c

m

OES Intensity ratio, I(Zn)/I(O)

Although the film resistivity data is not completely free from scattering [yet], the correlation between the values of the OES line intensities upon film deposition and the film properties confirms the usefulness of OES for the deposition process control of ZnO:Al films

Resistivity for ZnO:Al films deposited at different Zinc and Oxygen optical emission line intensity ratios.

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,00

10

20

30

40

50

60 Ar + O2

Ar + O2 + H

2 (5%)

Ar + O2 + H

2 (25%)

*10

-3, o

hm*c

m

IZn

/IZn(max)

Film resistivity as a function of Zinc optical emission line IZn/IZnmax ratio. The IZn/IZnmax ratio range corresponds to the oxygen flow range after the maximum in Zinc line intensity

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU

AcknowledgemenAcknowledgementsts

We are grateful to the

Eiropas Reģionālās attīstības fonda Eiropas Reģionālās attīstības fonda 2.1.1.1.aktivitātes „Atbalsts zinātnei un pētniecībai” 2.1.1.1.aktivitātes „Atbalsts zinātnei un pētniecībai”

2010/0272/2DP/2.1.1.1.0/10/APIA/VIAA/0882010/0272/2DP/2.1.1.1.0/10/APIA/VIAA/088http://www1.cfi.lu.lv/teor/ERAF/http://www1.cfi.lu.lv/teor/ERAF/

RSD2011 J.Purans – ISSP,LURSD2011 J.Purans – ISSP,LU