CE

Good bulk
transport
Poor interfacial
transport
Cu
Reactive
O
Magnetron
Sputtering:
O2
gas
flow
h+
Jonas Deuermeier,
PhD. Student
h+
> 200 nm Cu2O
Supervisors:
Prof. Elvira Fortunato (UNL)
Prof. Andreas Klein (TUD)
~ 12 nm Cu2O
Defects at interface
Objectives
What is responsible for limited device
Electronic defects? Diffusion?
performance of p-type oxide TFTs?
Where in the device?
How can we measure this?
Electrical characterization?
X-ray and ultraviolet
Photoelectron Spectroscopy
Photoelectron Spectroscopy on interface?
Can we overcome the limitations?
Mechanisms intrinsic to the material?
Complications induced by fabrication?
What can we do to improve devices?
Alternative combination of materials?
New device structures? … ?
chambers:
Magnetron
Atomic Layer
Deposition
Figure 1
Photolithography
Devices
Cu(0)
0.3-0.4
In situ X-ray and Ultraviolet
Transport properties
Photoelectron Spectroscopy (fig. 1)
Comparison of bulk and thin film Cu2O
EF
0.5
EF
0.2
0.3-0.4
2.8
Cu2O
4.5
*General characterization of material:
X-ray diffraction, Scanning Electron Microscopy,
Hall-Effect, UV-Vis-NIR Spectroscopy, ...
EVBM
Results
[eV]
Magnetron
Sputtering
More oxidized state (y>0) → more intrinsic acceptors VCu → higher hole concentration
Al2O3 by
[1]
Atomic Layer Deposition
→ Keep Cu2O stoichiometric, even down to the interface level
Top-gate geometry: Clear chemical damage to Cu2O channel by Al2O3 deposition
Al2O3 by
EVBM
Non-stoichiometric Cu2-yO:
•
Cu(II)
Cu2O
Chemical analysis and energy band alignment
of substrate and film
e-
hn
[2]
Figure 2
(fig. 2)
Al2O3 by Atomic Layer Deposition → reduction to Cu(0), Schottky-barrier formation
0
•
Al2O3 by reactive Magnetron Sputtering → oxidation to Cu(II), lower Fermi energy
-2
•
High Hall mobility (32 cm2/Vs) but low field-effect mobilty and on-off ratio in TFT (fig. 3)
•
In situ XPS: Cu(II) in Cu2O changes with increasing film thickness (fig. 4)
•
In progress: Temperature- and time-dependent electrical measurements of bulk Cu2O and TFTs
-4
-6
0.4
VD= -1V
W/L= 40/20 0.0
-10
-45 -30 -15 0 15 30
VG (V)
-8
0
-100
VG
6 steps
30 to -45 V
-200
2
Bottom-gate geometry: Evidence for defective growth of Cu2O on dielectric
0.8
-3
→ No working transistor devices
1.2
fe (10 cm /VS)
•
ID (nA)
Atomic Layer Deposition: gate dielectric Al2O3
UHV
Sputtering,
Methods and techniques
Reactive Magnetron Sputtering: p-type Cu2O*
Preparation
ID (nA)
-300
-40
-20
VD ( V)
Publications
[2] Deuermeier, J., Yanagi, H., Bayer, T. J. M., Martins, R., Klein, A., and Fortunato, E., Advanced
Materials Interfaces (submitted)
Figueiredo, V. , Pinto, J. V., Deuermeier, J., Barros, R., Alves, E., Martins, R., and Fortunato, E.,
J. Disp. Technol. 9, 735–740 (2013).
Bayer, T. J. M., Wachau, A., Fuchs, A., Deuermeier, J., and Klein, A., Chem. Mater. 24, 4503–
4510 (2012).
[1] Deuermeier, J., Gassmann, J., Brötz, J., and Klein, A., J. Appl. Phys. 109, 113704 (2011).
0
Figure 3
to tackle questions on defect mechanisms
0.05
Cu(II) in Cu2O (%)
CENIMAT – Materials Research Centre, New
University of Lisbon
Transparent p-type transistors based on Cu2O –
Understanding material properties to enhance
device performance
Cu/O:
1.98
1.91
2.05
2.05
2.11
0.04
0.03
0.02
0.01
0.00
1
10
thickness (nm)
100
Figure 4