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PECVD Grown Graphene as Transparent Electrode in GaN-based LEDs

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CONTACT PERSON REFERENCES
PECVD Grown Graphene as Transparent Electrode in GaN-based LEDs
Jan Mischke1, Joel Pennings1,2, Erik Weisenseel1, Philipp Kerger3, Michael Rohwerder3, Wolfgang Mertin1and Gerd Bacher1
1Werkstoffe der Elektrotechnik and CENIDE, Universität Duisburg-Essen, Duisburg, Germany,
2Faculty of Engineering, University of Waterloo, Waterloo, Canada
3Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany
Jan Mischke
jan.mischke@uni-due.de
PhD student
Electronic Materials and Nanostructures
Faculty of Engineering
University of Duisburg-Essen
47057 Duisburg, Germany
PECVD System
Typical process diagram
Direct growth of graphene on GaN via plasma-enhanced chemical vapor
deposition (PECVD) without H2atmosphere
Homogeneous gas flow
through the showerhead
Temperature control over
the bottom and top heater
(>1000 °C)
Pulsed DC plasma
operation with variable
frequency (1-100 kHz
possible)
Black Magic 4”
[1] K.I. Bolotin et al., Solid State Comm. 146 (2008) 351-355
[2] R.R. Nair et al., Science 320 (2008) 1308
[3] Z. Yun et al., Chinese Physics B 23 (2014) 096802
[4] M. A. Mastro et al., Journal of Crystal Growth 274 (2005) 38-46
[5] J. Mischke et al., 2D Materials 7 (2020) 035019
Plasma
We thank Hans Lugauer and Adrian Avramescu from OSRAM Opto
Semiconductors GmbH for their support during this work.
Jan Mischke acknowledges a scholarship from the International Max
Planck Research School for Interface Controlled Materials for Energy
Conversion (IMPRS-SurMat).
Joel Pennings acknowledges a research internship from the DAAD
RISE Germany program with corresponding funding by Mitacs
Canada.
ACKNOWLEDGMENTS
Using graphene as a transparent
electrode on GaN-based LEDs
Motivation
Idea: Switch from commonly used H2to N2
during graphene growth process
Idea
Use graphene as transparent electrode to increase lateral
current spreading of GaN-based LEDs
Challenge
Transfer-free processing of graphene directly on
AlxGa1-xN LEDs without the use of H2
Graphene offers outstanding properties
High charger carrier mobilities
(200.000 cm2V-1s-1) [1]
High optical transparency
(2.3% absorption per layer) [2]
GaN + 3
2H2Ga + NH3
“Reverse Epitaxy” destroys GaN
surface under H2rich atmosphere and
high temperatures
N2is known to protect the GaN surface
under elevated temperatures [4]
[3]
View into the inner chamber
500 nm
H2atmosphere shows distinctive etching of the
GaN surface even at lower temperatures
No graphene growth can be observed
Switching to N2atmosphere protects the GaN
surface from etching effects
Graphene growth under
N2atmosphere observed
Increasing 2D-peak with
increasing growth time
N2atmosphere shows promising results in protecting the GaN surface while
simultaneously supporting graphene growth
Influence of the CH4amount [5]
Growth time is crucial [5]
So does it work as intended? [5]
High CH4amount lead to distinctive etching of the GaN
surface due to free Hspecies
5 sccm to 200 sccm CH4:N2offers a good growth/etch
balance for graphene growth
I2D/IGratios of > 1.5 achieved
800 °C, X:200 sccm CH4:N2, 5 mbar, 1 h, 40 W
CH4:N2ratio influences the balance between graphene growth and surface etching
Graphene
Growth
Surface
Etching
H2vs. N2atmosphere [5]
With increasing growth time
Decrease of ID/IG& I2D/IGratios
Increase in FWHM of G & 2D peaks
Growth of multilayer graphene with increasing growth time
Tuning of the sheet resistance of the grown graphene layers
Sheet resistances of ~1 kΩ/
@ ~12% transparency losses
Graphene electrode shows largely increased
emission area across the LED surface
Diode-like behavior after growth process
500 µm
~8 times higher
emission
around contact
area compared
to LEDs without
graphene Scratched graphene
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