Bandgap Engineering of the Amorphous Wide Band-Gap

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Nov 1, 2013 (3 years and 9 months ago)

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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

Departamento de Ciencias


Sección Física


Grupo Ciencias de los Materiales

Pontificia Universidad Católica del
Perú (PUCP)

San Miguel, 14th
of
April 2011

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

Combine the advantages of an
insulator

and a
semiconductor

Principal idea:

Advantage of a semiconductor:

Advantage of an insulator:

Active
electronic devices

like diodes, transistors, etc

Due to the wide band
-
gap the samples are
transparent

Why wide band
-
gap semiconductors ?

Historic development:

GaN based LED

Band
-
gap engineering

Variation of the band
-
gap by changing the composition

The band
-
gap has influence on:




Emission wavelength of an optical device



efficiency of the light emission



energy level of the dopants



etc.

Choose an optimal composition for a specific application

A
x
B
1
-
x

Small overview of semiconductors

Wide band
-
gap


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





Colors in rare earth doped GaN

M. Garter et al. Appl. Phys. Lett.
74

(1999) p.182


Excitation mechanism

1 and 2: excitation paths

a and b: recombination paths

RE
3+

Ion

Cathodoluminescense of RE
3+


in
a
-
AlN:RE

Intrashell
-
transitions of f
-
shells

Temperature quenching of Er
3+

doped semiconductors

From
Favennec: Electronics Letters
25

(1989) 718

a)
In
0,16
Ga
0,38
As
0,84
P
0,16

b)
Si

c)
InP

d)
GaAs

e)
Al
0,17
Ga
0,83
As

f)
ZnTe

g)
CdS

Increase of band
-
gap

Temperature quenching for Er
3+

emission

From Zanatta:
Appl. Phys. Lett.
82

1395 (2003)


Temperature quenching in AlN:RE

From
Lozykowski and Jadwisienczak: Phys. Stat. Sol. B
244

(2007) 2109

Phenomenological description:

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

a
-
(SiC)
x
(AlN)
1
-
x
:RE

Why
a
-
(SiC)
x
(AlN)
1
-
x
?

Rare earth doping:




Well defined emission color



Covering of the whole color range



Wide bandgap semiconductors:




Increase of rare earth emission



Lower temperature quenching



Transparent



Semiconductor devices


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


Los principios de
dc
-
sputtering

target

ánodo

+

+

+

+

+

+

+

+

ion Ar

Átomo Ar

electrón

Plasma frío:

10
-
2
mbar

sustrato

-

+

Problemas:


Inestabilidad del plasma


Sólo targets metálicos


Baja eficiencia

1000 V

Los principios de
magnetrón
-
sputtering

Aumento de densidad de los iones

Más rapidez del crecimiento

El magnetrón

magnetrón armado

blindaje

portatarget

N

N

N

S

S

S

Anillo de plasma

target

Schematics of the sputtering system

Turbo
-
molecular
pump

Mechanical

pump

Pressure
sensor

Mass
spectrometer

control

Ar

N
2

Mass flow
controler

Control of

mass
spectrometer

Rf
-

generator

Rf
-
generator

shutter

H
2
O

substrate

targets

flexible

magnetrons

H
2
O

match

PC control

The rf magnetron sputter system at the PUCP

Vacuum system:






residual gas analysis


Gas processing:



flow control of
N
2
, H
2

and
Ar:


0…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 cm
2



variable target substrate distance



water cooled substrate holder

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

a
-
SiC

3
´

3
´

80403

80402

80401

80331

80327

Característica de emisión de un magnetrón I

Característica de emisión de un magnetrón II

N

N

N

S

S

S

1cm

emisión en uu. aa.

Contorno de emisión

blindaje

plasma

target

imanes

A typical thin film of
a
-
(SiC)
x
(AlN)
1
-
x

EDX results



highly pure films (i.e. Na content < 8 ppm wt.)



no signature of impurities in the film

host

substrate

Transmission electron microscopy (TEM):

Structure of
a
/
nc
-
AlN and
a
-
SiC anealed at 900
°
C

High resolution transmission electron microscopy (HRTEM):

There are
nanocrystals

embedded


in an
amorphous matrix

Substrate (Si)

a
-
SiC

diffraction

a/nc
-
AlN

a/nc
-
AlN

Optical absorption measurements

Determination of the band
-
gap i.e.
a
-
(SiC)
0.25
(AlN)
0.75

:

Band
-
gap engineering of
a
-
(SiC)
x
(AlN)
1
-
x

[1]
Nurmagomedov

et al.:
Sov
. Phys.
Semicond
.
23

100 (1989)

[2]
Gurumurugan

et al.: Appl. Phys.
Lett
.
74

3008 (1999)

[3]
Zanatta

et al.: J. Phys. D: Appl. Phys.
42
(2009) 025109

Bowing parameters:
b

2
=
(1.98
±
0.94) eV ,
b
T
auc
=
(1.96
±
0.48) eV

Fitting to Vegard
´
s law:

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

Emission of rare earth ions in
a/nc
-
AlN and
a
-
SiC

Cathodoluminescense of RE
3+


in
a
-
AlN:RE

Cathodoluminescense of RE
3+


in
a
-
SiC:RE

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

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 Tb
3+

emission in
a
-
SiC

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


Thermal activation of
a
-
(SiC)
0.83
(AlN)
0.17
:Tb
3+

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




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
)

Wide bandgap semiconductors

From Steckl MRS Bull.
24,

p. 33 (1999)