The effect of oxygen on the properties of co-sputtered Zn-Ir-O thin films
M. Papadaki
(1)
, G. Michail
(1)
, V. Kambylafka
(1)
, K. Tsagaraki
(1)
, M. Androulidaki
(1)
,
G. Kiriakidis
(2,3)
, M. Modreanu
(3)
and E. Aperathitis
(*,2)
(1)
Institute of Electronic Structure & Laser, Foundation for Research and Technology–
FORTH-Hellas, P.O. Box 1385, Heraklion 70013, Crete, Greece.
(2)
Physics Department, University of Crete, P.O. Box 2208, 71003 Heraklion, Crete, Greece.
(3)
Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland.
Corresponding & Presenting Author: E. Aperathitis,
ZnO is a wide band gap semiconductor, with high exciton binding energy, good
transparency and its conductivity (when doped with Al) approaches that of the widely used n-
type indium-tin-oxide (ITO). As a result, ZnO is the ideal material to replace ITO on many
applications in the emerging field of transparent electronics and optoelectronics. ZnO exhibits
intrinsic n-type conductivity but achieving p-type ZnO in a controllable, reproducible and
reliable manner remains a technological challenge. Recently, theoretical calculations [
D.
Munoz Ramo, et al, “Hybrid density functional calculations of the defect properties of
ZnO:Rh and ZnO:Ir”, Thin Solid Films 555 (2014) 112
] have shown that while low Ir doping
of ZnO can lead to hole trapping processes inhibiting p-type conduction and transparency,
high Ir concentrations reduce diffusion barriers for hole hopping through the lattice and thus
Zn-Ir-O can give rise to p-type conductivity. Sputtered ZnO-IrO
2
films [
M. Zubkins, et al,
“Structrural, electrical and optical properties of zinc-iridium thin films deposited by DC
reactive magnetron sputtering”, Phys. Stat. Solid. C 11 (2014) 1493
], containing more than
35 at.% Ir, exhibited resistivity of around 10
-3
Ωcm but the transmittance at 550 nm was not
more than 33%. Only after annealing these films in air at 500
o
C for 20 hours the
transmittance was increased to 60% with no appreciable change in resistivity.
In a previous investigation we had shown [G. Michail, et al., “
On the growth of
transparent conductive oxide ternary alloys Zn–Ir–O (ZIRO) by the means of rf magnetron
co-sputtering
”, Thin Solid Films (2016),
] that co-
sputtering of ZnN target with Ir pellets on it in a mixed argon and oxygen plasma can give
Zn-Ir-O films (ZIRO) whose Ir content depends on the amount of oxygen in Ar plasma. By
increasing the amount of oxygen up to 10% in plasma the content of Ir was saturated to
around 3.3 at.%. Furthermore the structural and optical properties of the highly resistive films
were found to deteriorate upon annealing in forming gas containing %N
2
-H
2
at elevated
temperatures up to 700
o
C,.
In this presentation we are going to show that excess oxygen plasma during deposition
reduces the amount of Ir in ZIRO films regardless the number of Ir pellets used on the surface
of ZnN target. ZIRO films containing 1-10 at.% of Ir were fabricated and their structural,
optical and electrical properties were examined by AFM, FE-SEM & EDX, GI-XRD,
spectroscopic techniques (UV-VIS-NIR transmittance, Raman and variable angle
ellipsometry) and Hall-effect measurements, respectively. Preliminary results have revealed
that, upon annealing the ZIRO films in nitrogen environment, the transparency is reduced but
the dominant carriers of conduction were holes thus making ZIRO films p-type oxides.
*
PS2 33
-227-
