Electronic states of a-In-Zn-O films analyzed
by x-ray photoelectron andreflected electron energy loss spectroscopies
It is important to investigate the electronic states of transparent conductive oxide (TCO) films toacquire the directions for electrical property control and device development. In this study, weinvestigated the electronic states of indium zinc oxide (IZO) films deposited under different oxygen
flow ratios . The influence of oxygen flow ratios on the electrical properties of IZO films is discussed
on the basis of the results obtained by electron spectroscopies.
1. Samples and analyses

2. Optical band gap（REELS）

The Carrier density
increases with a decrease
ofthe oxygen flow ratio.（１）
4.0

3.0
2.0
Flow Ratio (％）

1.0

EVAC
ECBM

(１) T. Ashida et al. J. Vac. Sci.
Technol. A25(4), 1178(2007).

0.0

e-Analyses ・Optical band gap： Reflected electron energy loss

EFEVBM

spectroscopy (REELS)
・Valence band region and work function：
X-ray photoelectron spectroscopy (XPS)

WF（or IP )=hν－{ EK（VBM)－EK（0）}In cacuum

XPSspectrum(schematic daigram )X線(hν）e-hν
EVBM WF (or IP)
XPS : X-ray photoelectron spectroscopy,
WF : Work function, IP : Ionization potential,
EK : Kinetic energy

Valence band

12.0

10.0

EK(0) Region

Intensity (arb. units)

EFEg(Opticalband gap)

REELS
0%：3.1±0.1 eV
1%：2.9±0.1 eV
5%：2.8±0.1 eV
8.0

6.0
4.0
2.0
Loss Energy (eV)

0.0

0%
1%
5%
normalized by Au at 5.10 eV.

Kinetic energy

EK(VBM)WF (eV）

0%

4.41%

4.65%

4.8

・The work function energies wereEVAC

EK(0)O2 flow4.0

4.5
5.0
Kinetic Energy (eV)5.5

As the carrier density increases,
the work function decreases.

5. Correlaton of results◆ The high sensitivity XPS measurement using a magnetic field
condensing type electron lens are demonstrated.
Valence bandO2 flow 0%
In gap states
O2 flow 1%
O2 flow 5%0%1%◆ The relationship between electronic states and peak intensity
near the Fermi level

Intensity (arb. units)

4. Valence band region（XPS）

6.0-2.0 4.0

4.0
2.0
0.0
Binding Energy (eV)

3.0

2.01.00.0
Binding Energy (eV)As the carrier density increases,
the peak intensity near the Fermi level increases.

6. Energy band diagram
EVACConduction band

WF=4.8 eV

WF=4.6 eV

WF=4.4 eV

Eg=2.9 eV

Eg=3.1 eVEF

The electronic statesnear the Fermi level

Eg=2.8 eVValence bandO2 flow 5%
Carrier density （１）O2flow 1%

1018 cm-35%
1%5%Expand

8.0-2.0

EF : Fermi energy, EVAC : Vacuum energy, EVBM : Valence band maximum energy, Eg : Optical band gap,
ECBM : Conduction band minimum energy, REELS : Reflected electron energy loss spectroscopy◆ The lowest kinetic energy of photoelectrons is measured.
InternalsubstanceInteraction

As the carrier density increases,
the optical band gap slightly increases.

3. Work function （XPS）
Electron density of state（schematic daigram）

Conduction band

Intensity (arb. units)-3

1.0E+211.0E+20
1.0E+19
1.0E+18
1.0E+17
1.0E+16
1.0E+15
1.0E+141.0E+135.0◆ The scattering electron energy loss between the conduction band
minimum and the valence band maximum is measured.
LossEnergy

Carrier Density (cm )Sample ： IZO film /Si sub.
Oxygen flow ratio (O2/Ar+O2) ： 0%, 1%, 5%
Total gas pressure of Ar (99.999%)：0.7 Pa

O2flow 0%-1.00%As the peak intensity
near the Fermi level
increases ,the optical band gap
increases and the work
function decreases.
↓Interrelations are related
to BM effect

BM ： Burstein-Moss◆ Extrapolating from carrier density,
Fermi level should be located in conduction band at 0% and 1%.
Fermi level should be located in band gap at 5%.
◆ The relationship between film forming conditions (carrier density)and electronic states was investigated systematically.
↓It is important to understand energy band diagram
for clarification of the electronic property of TCO.
※This study is a result of joint research with Y. Shigesato of graduate school of Science
Engineering , Aoyama Gakuin University.

Toray Research Center, Inc.

P00846表面解析第１研究室20110831
STC：開(20110831)