Al-doped ZnO: RF- or DC-sputtering?
Andrea Crovetto
(1) *
, Tobias Ottsen
(1)
, Eugen Stamate
(2)
, Daniel Kjær
(3)
, Jørgen Schou
(4)
,
Ole Hansen
(1,5)
(1)
DTU Nanotech, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
(2)
DTU Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark
(3)
CAPRES A/S, Scion-DTU, DK-2800 Kgs. Lyngby, Denmark
(4)
DTU Fotonik, Technical University of Denmark, DK-4000 Roskilde, Denmark
(5)
CINF, Center for Individual Nanoparticle Functionality, Technical University of Denmark,
DK-2800 Kgs. Lyngby, Denmark
* Presenting author. Address: DTU Nanotech, Ørsteds Plads, building 344, room 030, DK-
2800 Kgs. Lyngby, Denmark phone: +45 45255845, fax: +45 45887762, email:
The electrical properties of ZnO:Al thin films grown by sputtering often depend on
deposition pressure and position on the substrate. For RF sputtering, we recently showed that
the electrical properties are, at a more general level, quantitatively correlated to changes in
compressive stress in the films and partially to gradients in oxygen content [1]. Grain size,
texture, and Al content were also observed to be generally dependent on compressive stress.
In this work, we add newly characterized properties and new data from DC-sputtered ZnO:Al
films to the picture. This allows a parallel comparison of the trends in the ZnO:Al film
properties with the two different sputtering methods. In particular, we see that both
compressive stress (determined by x-ray diffraction peak position) and microscopic strain
(determined by detailed analysis of x-ray diffraction peak broadening) are in general larger in
DC-sputtered films than in RF-sputtered films, but their spatial distributions are similar. On
the other hand, a number of film properties (including grain size and texture coefficient) do
not follow the same spatial distributions in RF- and DC sputtering. A particularly interesting
effect is that the depth-resolved distribution of the dopant (aluminum) changes significantly
depending on deposition conditions. Even though inhomogeneity in aluminum content
through the depth of ZnO:Al films has been investigated before [2], it has not been related
systematically to the deposition conditions, nor to the resulting electrical properties.
By highlighting the changes in film properties and by reviewing the expected differences in
ion bombardment effects between RF- and DC-sputtering, we propose slightly different
physical mechanisms at the origin of inhomogeneity in the electrical properties of ZnO:Al
deposited with the two sputtering methods.
[1] A. Crovetto
et al.
,
J. Phys. D. Appl. Phys.
49
, 295101 (2016).
[2] Bikowski
et al.
,
APL Mater.
3B
060701 (2015).
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