1. Bandgap Engineering of the Amorphous Wide Band-Gap Semiconductor (SiC)1-x(AlN)x Doped with Rare Earths and its Optical Emission Properties
Roland Weingärtner
San Miguel, 14th of April 2011
Departamento de Ciencias – Sección Física – Grupo Ciencias de los Materiales
Pontificia Universidad Católica del Perú (PUCP)

2. Outline I Motivation and Introduction Wide band-gap semiconductors
Band-gap engineering
Rare earth doping and optical emission
II First Results of a-(SiC)x(AlN)1-x
Thin film growth method and structural characterisation
Band-gap engineering of a-(SiC)x(AlN)1-x
III Cathodoluminescense measurements
Spectral emission of rare earth doped a-(SiC)x(AlN)1-x
Thermal activation of rare earth emission
IV Summary and Acknowledgements

3. Why wide band-gap semiconductors ?
Principal idea:
Combine the advantages of an insulator and a semiconductor
Advantage of a semiconductor:
Active electronic devices like diodes, transistors, etc
Advantage of an insulator:
Due to the wide band-gap the samples are transparent
Historic development:
GaN based LED

4. Example: Silicon Carbide (c-SiC)
High power electronics:
Schottky diode with high breakdown voltage
Reduction of space and costs
in a power source unit of a PC
Band
gap
Breakdown voltage
SiC
3.0 eV
5 MVcm-1 Si
1.1 eV
0.3 MVcm-1
Other applications:
optoelectronics
High frequency electronics
High temperature devices

5. Band-gap engineering AxB1-x The band-gap has influence on:
Emission wavelength of an optical device
efficiency of the light emission
energy level of the dopants
etc.
AxB1-x
Variation of the band-gap by changing the composition
Choose an optimal composition for a specific application

6. Small overview of semiconductors
Wide band-gap

7. Why rare earth doping in semiconductors ?
Optical emission properties of rare earths:
emission wavelength does not depend on the host material
Color is typical for a specific rare earth ion
Intensity of rare earth emission depends on the material:
band-gap quenching
temperature quenching
concentration quenching

8. Colors in rare earth doped GaN
M. Garter et al. Appl. Phys. Lett. 74 (1999) p.182

9. Cathodoluminescense of RE3+
Excitation mechanism
Cathodoluminescense of RE3+
in a-AlN:RE
Intrashell-transitions of f-shells
RE3+ Ion
1 and 2: excitation paths
a and b: recombination paths

10. Temperature quenching of Er3+ doped semiconductors
In0,16Ga0,38As0,84P0,16 Si
InP
GaAs
Al0,17Ga0,83As
ZnTe
CdS
Increase of band-gap
From Favennec: Electronics Letters 25 (1989) 718

11. Temperature quenching for Er3+ emission
From Zanatta: Appl. Phys. Lett (2003)

12. Temperature quenching in AlN:RE
Phenomenological description:
From Lozykowski and Jadwisienczak: Phys. Stat. Sol. B 244 (2007) 2109

13. Outline I Motivation and Introduction Wide band-gap semiconductors
Band-gap engineering
Rare earth doping and optical emission
II First Results of a-(SiC)x(AlN)1-x
Thin film growth method and structural characterisation
Band-gap engineering of a-(SiC)x(AlN)1-x
III Cathodoluminescense measurements
Spectral emission of rare earth doped a-(SiC)x(AlN)1-x
Thermal activation of rare earth emission
IV Summary and Acknowledgements

14. a-(SiC)x(AlN)1-x:RE Why a-(SiC)x(AlN)1-x? Wide bandgap semiconductors:
Increase of rare earth emission
Lower temperature quenching
Transparent
Semiconductor devices
Rare earth doping:
Well defined emission color
Covering of the whole color range
a-(SiC)x(AlN)1-x:RE
Amorphous films:
Inexpensive
Simple production
Higher incorporation of rare earths
Pseudobinary compound:
Band-gap engineering (3eV to 6eV)
one composition parameter
Sputtering from SiC and AlN target

15. Los principios de dc-sputtering
target
sustrato +
10-2 mbar + +
1000 V + + + +
ánodo + +
ion Ar
Átomo Ar
electrón
Plasma frío:
Problemas:
Inestabilidad del plasma
Sólo targets metálicos
Baja eficiencia

16. Los principios de magnetrón-sputtering
Aumento de densidad de los iones
Más rapidez del crecimiento

17. El magnetrón portatarget blindaje Anillo de plasma target
magnetrón armado S N S S N N

18. Schematics of the sputtering system
Mass spectrometer
Control of mass spectrometer
H2O
shutter
Mass flow controler
substrate
targets
Pressure sensor
Rf- generator
Rf-generator
flexible
magnetrons
Turbo-molecular pump
H2O
match
Mechanical pump
control
PC control Ar N2

19. The rf magnetron sputter system at the PUCP
Vacuum system:
residual gas analysis
Gas processing:
flow control of N2, H2 and Ar: …100 sccm, 5N...6N
working pressure:
Sputter targets:
trial magnetron sputtering, 2´´
3 Rf generators, P<300W
felxible target geometry !!
Substrates:
Substrate area up to 128 cm2
variable target substrate distance
water cooled substrate holder

20. A typical film of a-SiC on glas
Target material:
Silicon Carbide (SiC)
Substrate material:
fused glas
Rf power:
100 W
Process gas:
Argon, 5N
Gas flow:
80 sccm
Argon pressure:
810-3 mbar 3´
a-SiC 3´

21. Característica de emisión de un magnetrón I
80403
80402
80401
80331
80327

22. Característica de emisión de un magnetrón II
emisión en uu. aa.
Contorno de emisión
1cm
plasma
target S N S
blindaje S N N
imanes

23. A typical thin film of a-(SiC)x(AlN)1-x
EDX results
host
substrate
highly pure films (i.e. Na content < 8 ppm wt.)
no signature of impurities in the film

24. Structure of a/nc-AlN and a-SiC anealed at 900°C
Transmission electron microscopy (TEM):
diffraction
a/nc-AlN
a-SiC
Substrate (Si)
High resolution transmission electron microscopy (HRTEM):
a/nc-AlN
There are nanocrystals embedded
in an amorphous matrix

25. Optical absorption measurements
Determination of the band-gap i.e. a-(SiC)0.25(AlN)0.75 :

26. Band-gap engineering of a-(SiC)x(AlN)1-x
[1] Nurmagomedov et al.: Sov. Phys. Semicond (1989)
[2] Gurumurugan et al.: Appl. Phys. Lett (1999)
[3] Zanatta et al.: J. Phys. D: Appl. Phys. 42 (2009)
Fitting to Vegard´s law:
Bowing parameters: ba2=(1.98±0.94) eV , bTauc=(1.96±0.48) eV

27. Outline I Motivation and Introduction Wide band-gap semiconductors
Band-gap engineering
Rare earth doping and optical emission
II First Results of a-(SiC)x(AlN)1-x
Thin film growth method and structural characterisation
Band-gap engineering of a-(SiC)x(AlN)1-x
III Cathodoluminescense measurements
Spectral emission of rare earth doped a-(SiC)x(AlN)1-x
Thermal activation of rare earth emission
IV Summary and Acknoledgements

28. Emission of rare earth ions in a/nc-AlN and a-SiC
Cathodoluminescense of RE3+
in a-AlN:RE
Cathodoluminescense of RE3+
in a-SiC:RE

29. Thermal activation of a-/nc-AlN
exponential growth with the anealing temperature
there is a saturation of the RE emission at anealing tempertures of 900°C

30. Thermal activation of a-SiC
exponential growth with anealing temperature
there is no saturation up to 1000°C
there is an optimal anealing temperature for the Tb3+ emission in a-SiC

31. Thermal activation of a-(SiC)x(AlN)1-x

32. Thermal activation of a-(SiC)0.83(AlN)0.17:Tb3+

33. Summary Wide-bandgap semiconductors Rare earth doping
bandgap engineering
First results on a-(SiC)x(AlN)1-x thin films
HRTEM investigations
bandgap engineering of a-(SiC)x(AlN)1-x
Cathodoluminescense
optical emission of a-(SiC)x(AlN)1-x
thermal activation of rare earth emission
Conferences/Publications:
IMRC 2009 in Cancun, Mexico (invited talk)
ICSCRM´2009 in Nuremberg, Germany
Five publications in International Journals

34. Acknowledgements Materials Department, University of Erlangen, Germany
Prof. Dr. Winnacker
Prof. Dr. H. P. Strunk
Catholic University of Lima, Peru (PUCP)
Prof. F. De Zela
Andrés Guerra, Gonzalo Galvez, Oliver Erlenbach (PhD)
Liz Montañez, Katia Zegarra, (Licenciatura)
This research work is supported by the
Pontificia Universidad Católica del Peru (PUCP)
Deutsche Forschungsgemeinschaft (DFG) and the
German Service of Academic Interchange (DAAD)

35. Wide bandgap semiconductors
From Steckl MRS Bull. 24, p. 33 (1999)