Extended X-ray Abso rptio n Find-Struc ture Investigation o f-FeSi2
CarbonTarek M. Mostafa1, Mahmoud Shaban2, Motoki Takahara1, Suguru Funasaki1, Aki Tominaga1,Toshihiro Okajima3, and Tsuyoshi Yoshitake1
1Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
2Department of Electrical Engineering, Aswan Faculty of Engineering, Aswan University, Aswan 81542, Egypt
3Kyushu Synchrotron Light Research Center (SAGA-LS), Tosu, Saga 841-0005, Japan

ABSTRACT
Semiconducting iron disilicide -FeSi2 has recently attracted considerable attention from both scientists and engineers due to its remarkable optical and electrical-FeSi2/Si heterojunctions to be employed near infrared photodiode. Thier hetrojunctions showed typical rectifying actions. However,their current-voltage (I-V) characteristics exhibited large leakage dark current. We believe that the main source of its large leakage current is the high carrier-FeSi2 epitaxial film. In previous study, we found that C-FeSi2 might be an effective for reducing the carrier density somehow. In this study,-FeSi2 As a firstextended X-ray absorption find-structure (EXAFS) measurement was employed in order to investigate the local-bonding structure of Cstep of the EXAFS evaluation, a change in the EXAFS spectrum for the substrate temperature was studied in order to verify the availability of EXAFS analysis for
C-doped -FeSi2.

INTRODUCTIONc

Near Infrared Rays

Research AIMbFe

Pd electrodeEvaluate

Si-FeSi2 defined as a ecofriendly asemiconductor is regarded as one ofthe 3-rd generation semiconductors
after Si and GaAs.
-FeSi2 has a large absorption
coefficient, and possesses indirect
and direct optical band gaps of 0.74
eV and 0.85 eV, respectively.
-FeSi2 can fabricate a variety ofdevices as energy devices, solar cells
and thermoelectric generator can beproduced and as optoelectronicdevices, photodiodes and lightemitting diodes both operating nearinfrared (NIR) -up to the wavelength- can be made.
of 1.55
Previously,-FeSi2 havebeen
epitaxial grown on Si(111)substrates
at a substrate temperature 600 C byfacing-targets direct-current sputtering(FTDCS)
andradio-frequency
magnetron sputtering (RFMS) to form
Sin-type-FeSi2/p-Typeheterojunctions diodes.

a = 0.986 nm
b = 0.779 nm
c = 0.783 nm

Ligure RN

510FeSi2 films formed o n Si(111) by RFMS
and c larify how growth temperature
influenc e the film quality and theElec tric al pro perties of the n-type FeSi2/p-Type Si hetero junc tions.

XAFS measurement used
by Kyushu university
beamline(BL6) at SAGALS
Measurement metho ds:
Conversio n Elec tro n Yield(CEY)

p-type Si(111)n-type -FeSi2
Al electrode

Ligure MN

2410310-FeSi2

AlPd

Substrate
temperature

600 - 500
(20 step)

R.T.

R.T.

Pressure

10-1 Pa210Si

1100100.8

11.2

Photo Energy (eV)Ligure TN

1010illumination current
dark current

2.66

6.65

10-1 Pa2.66 10-1 Pa

Electric power

20 W

100 W

50 W

Film thickness

300 nm

250 nm

250 nm

Ar gas flowrate

15sccm

5sccm

5sccm

10300 K
1001Voltage [ V ]using Athena and Artemis
softwareLigure VN

RESULTS and DISCUSSIONXRD measurements
To investigate the epitaxial growth and crystallinity of thedeposited films, they were characterized by XRD (Rigaku,RINT2000/PC) using 2 - , , and pole figure measurement
techniques.

measurement
We confirm that the rectifying action isexist at 600 ~ 540 C substratetemperature.
With reducing the temperature than
540 C the rectifying action isdramatically decrease, that it showed
an ohmic behavior at 500 C substratemeasurement

Ligure ^because of the degradation in thecrystallinity with reducing thetemperature.

Ligure Y.

The-FeSi2
deposited on Si(111)
Substratewith Temp. 560 Cheterojunctions
showedasignificant
improvementinleakagecurrent
andhighresponse
underillumination of 1.3m light.

Ligure Q

Ligure R_-LeSiTThe 202/220 peak of -FeSi2 was observed at 29 until
560 C.
For 2 method, Except -FeSi2 film of 520
C, thediffraction peaks were observed at all substratetemperatures.
Ligure Z
At 600 C, the.
202/220 peak of Ligure RR
0.5%at C-doped -FeSi at different[ O\[ ]USIO\wasFeSi2temperatures
observed.
-FeSi2 /Si heterojunctions were fabricated by RFMS at different temperatures.
For the 580 C andThe film was formed at 600 ~ 560 C substrate temperature, but -FeSi2 film included
560Cstate
multi-crystalline component.
patterns the peaks
Due to the defects, lattice mismatch, and Fe atoms diffusion in the Si substrate weare not separated.
found low directivity, and high leakage current which showed high improvement forThe peak of the 560 C deposition temperature. Depend on the above results 560 C deposition
wasnotFeSi2
temperature is confirmed as an optimum deposition temperature for -FeSi2 /Si
observed 500 C
heterojunctions for the ongoing research.
and540C
As a result of changing the conditions of thin films, there is a change in the portion ofLigure W
substrate
the vibration on Fe-Fe.
.
temperature.
Acknowledgement2

2013IIIK018.