Towards ptype doping of ZnO

1
Towards p-type doping of ZnO
The Australian National University Research
School of Physical Sciences and Engineering

• V. A. Coleman, H. H. Tan, C. Jagadish
• Department of Electronic Materials Engineering,
  The Research School of Physical Sciences and
  Engineering, The Australian National University,
  Canberra
• M. R. Phillips
• Microstructural Analysis Unit, University of
  Technology Sydney
• S. O. Kucheyev
• Lawrence Livermore National Laboratory,
  Livermore, USA
• J. Zou
• Division of Materials, School of Engineering, The
  University of Queensland, Brisbane

Department of Electronic Materials Engineering
2
Outline
The Australian National University Research
School of Physical Sciences and Engineering

• Introduction
• Experimental details
• Results and discussion
• Investigation of dopant activation / extended
  studies
• Concluding remarks and future work

Department of Electronic Materials Engineering
3
Motivation
The Australian National University Research
School of Physical Sciences and Engineering

• ZnO is a very attractive material for a large
  range of optoelectronic devices (Eg3.4
  eV, Exciton Binding Energy 60 meV)
• P-type doping is still a major challenge
• Ion implantation is widely used in the
  microelectronics industry for both doping and
  device isolation
• Understanding of damage accumulation and
  recrystallization processes is important

Department of Electronic Materials Engineering
4
This Work
The Australian National University Research
School of Physical Sciences and Engineering

• Implanted c-axis single crystal ZnO (n-type,
  Cermet) with Arsenic (p-type dopant!!) ions.
  Aimed to place most of the damage close to the
  surface.
• Annealing studies to achieve recrystallization
• Monitor recrystallization, damage accumulation
  and annihilation behaviour with RBS/C, XTEM and
  CL

Department of Electronic Materials Engineering
5
Implantation
The Australian National University Research
School of Physical Sciences and Engineering

• ZnO Single Crystals were implanted with 1.4 x
  1017 As/cm2 at 300 keV in the ANU 1.7 MV tandem
  accelerator at RT

Full TRIM calculation of the damage produced by
300 keV As ions implanted into ZnO at 7o. Plot
also shows As distribution. Peak As distribution
is at 106 nm (peak concentration of 1.4x1022
As/cm3)
Department of Electronic Materials Engineering
6
The Australian National University Research
School of Physical Sciences and Engineering

• Rutherford Backscattering Spectrometry-Channeling
  Spectra (RBS/C)
• 300 keV As ions ZnO single crystals

E
n
e
r
g
y
(
M
e
V
)
1
.
0
1
.
5
2
.
0
4
0
3
0
d
l
e
i
Y
d
e
z
2
0
i
190nm
l
a
m
r
o
N
1
0
0
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
6
0
0
C
h
a
n
n
e
l
Backscattered (170o)
Glancing (10o)
Department of Electronic Materials Engineering
7
The Australian National University Research
School of Physical Sciences and Engineering

• XTEM image of 300keV 1.4x1017 As/cm2 implanted
  layer

Close to crystalline material near the surface
surface
heavy damage
Voids?? 20nm in size
bend contour (crystalline material)
Department of Electronic Materials Engineering
8
Annealing Studies
The Australian National University Research
School of Physical Sciences and Engineering

• RTA and furnace annealing of samples. In all
  cases samples were proximity capped with ZnO
  epilayers to inhibit surface degradation, and
  annealing was carried out under Ar ambient.
• RTA for 60 seconds up to temperatures of 1000oC
  was insufficient to achieve complete
  recrystallization
• Higher temperatures (up to 1200oC) and longer
  times (15 mins) needed for recrystallization

Department of Electronic Materials Engineering
9
The Australian National University Research
School of Physical Sciences and Engineering

• RBS/C spectra of furnace annealed (15mins, Ar
  ambient) samples implanted with 300keV As ions
  showing evolution of recrystallization

Backscattered
Department of Electronic Materials Engineering
10
The Australian National University Research
School of Physical Sciences and Engineering

• XTEM of sample annealed at 1000oC for 15 mins
  under Ar

voids agglomerating
dislocations
voids
Department of Electronic Materials Engineering
11
The Australian National University Research
School of Physical Sciences and Engineering

• XTEM of sample annealed at 1100oC for 15 mins
  under Ar

voids migrating to the surface
surface
dislocations
Department of Electronic Materials Engineering
12
The Australian National University Research
School of Physical Sciences and Engineering

• XTEM of sample annealed at 1200oC for 15 mins
  under Ar

surface
remaining voids
dislocations caused by Heating!!!
Department of Electronic Materials Engineering
13
Cathodoluminescence (CL) Studies
The Australian National University Research
School of Physical Sciences and Engineering

• CL is used for probing near band edge (excitonic)
  emission and thus examining the optical
  properties of the recrystallized layers

Department of Electronic Materials Engineering
14
The Australian National University Research
School of Physical Sciences and Engineering

• CL spectra (15kV, 77K) Arsenic implanted ZnO

1000oC Anneal
1200oC Anneal

Department of Electronic Materials Engineering
15
Co-Implantation Studies
The Australian National University Research
School of Physical Sciences and Engineering

• High dose of Arsenic (1.4 x1017 As/cm2)
• Add 9x1019 cm-3 N for doping (dose of 2x1015
  N/cm2)
• N is currently thought to be one of the most
  promising p-type dopants for ZnO
• Ion energies were chosen to ensure profiles
  overlap
• 770keV As and 190keV N
• Anneal at 1000oC for 15 minutes under Ar

Department of Electronic Materials Engineering
16
The Australian National University Research
School of Physical Sciences and Engineering

• RBS/C of co-implanted layers

random
Backscattered Detector
1.4x1017 Ascm-2 and 2x1015 Ncm-2
1000oC anneal
Department of Electronic Materials Engineering
17
The Australian National University Research
School of Physical Sciences and Engineering

• CL spectra (30keV, 77K)

1000oC Anneal
Department of Electronic Materials Engineering
18
Conclusions
The Australian National University Research
School of Physical Sciences and Engineering

• ZnO is not completely amorphized by high dose
  (1.4x1017 cm-2) Arsenic implants
• Creation of a heavily damaged layer extending to
  a depth of 150 nm
• Region of voids ( 200 nm below the surface)
• Recrystallization occurs at higher temperatures
  (1200oC) by void migration and exfoliation of
  the surface
• Optical properties of ZnO are recovered following
  recrystallization

Department of Electronic Materials Engineering
19
Future Work
The Australian National University Research
School of Physical Sciences and Engineering

• AFM measurements over the implanted/unimplanted
  interface
• Repeat the work for epilayers
• Electrical characterization of implanted layers
  to check for p-type activation (epilayers)
• Implantation with O or Zn ions and then N
• Check ordering effect of co-implantation
• Annealing under O ambient

Department of Electronic Materials Engineering
20
Acknowledgements
The Australian National University Research
School of Physical Sciences and Engineering
Adam Sikorski The University of Sydney (TEM
sample preparation) Fred Johnson The
Australian National Univ. (Ion Beam Technical
Support) Tim Senden The Australian National
University (AFM)
Department of Electronic Materials Engineering
21
SIMS
The Australian National University Research
School of Physical Sciences and Engineering
Uncapped
SiO2 Capped 150 nm

Recrystallized (1200C)
100000
As-Implanted
10000
Counts (arb. units)

1000
100
10
0
100
200
300
400
500
Depth (nm)
Department of Electronic Materials Engineering