Cation-doped Cu
2
O as a transparent p-type semiconducting oxide with enhanced
performances: A comparison between strontium and magnesium incorporation
J. Resende
1,2
, S. Brochen
1
, L. Bergerot
1
, C. Jiménez
1
, N. D. Nguyen
2
, J. L. Deschanvres
1
1
Laboratoire des Matériaux et du Génie Physique, Univ. Grenoble Alpes, LMGP, F-38000 Grenoble,
France; CNRS, LMGP, F-38000 Grenoble, France
2
Solid State Physics, Interfaces and Nanostructures, Institut de Physique B5a, Allée du Six Août 19,
B-4000 Liège, Belgique
In the group of semiconducting metallic oxides, cuprous oxide (Cu
2
O) presents promising
electrical and manufacturing features for a variety of applications as p-type transparent material
suitable in the domains of transparent electronics and photovoltaic cells. However Cu
2
O suffers from
optical and electrical limitations, due to a relatively small bandgap of 2.17 eV and a fairly high
resistivity (> 10
2
.cm) in intrinsic thin films at room temperature.
In this work, we successfully doped Cu
2
O thin films with different divalent cations, namely
Sr and Mg, by metal-organic chemical vapour deposition. We compared the effects of each element
on crystallographic structure, films morphology, electronic transport and optical transmittance. In
both cases, the presence of the cation contributed to a higher stability of the Cu
2
O phase, reducing the
appearance of CuO parasitic phase. Nevertheless, a SrCO
3
phase was detected in the Sr doped system.
In terms of electrical properties, the incorporation of Sr, up to 16%, reduced the resistivity down to
1
.cm, with a mobility of 16 cm
2
.V
-1
.s
-1
. Moreover, the incorporation of strontium also leads to the
emergence of a with a deep acceptor level located around E
A
= 278 ± 21 meV above the top of the
valence band. The concentration of this deep acceptor level, attributed to simple copper vacancies,
drastically increases with the strontium content, due to a decrease of its formation energy. The effect
on optical transmittance could not be detected. The Mg-doped Cu
2
O thin films were monophasic and
showed a higher resistivity of 6.6
.cm at an Mg concentration of 17%, due to the lower mobility, 1
cm
2
.V
-1
.s
-1
. Although, the presence of this dopant contributes for the highest charge-carrier density
observed in this work, up to 8x10
17
cm
-3
. As in the Sr case, this can be explained by a simple copper
vacancy doping mechanism assisted by cation incorporation. Additionally, a slight increase of
transparency is observed when compared to intrinsic Cu
2
O.
The control of carrier concentration and mobility values by dopant concentration, as well as
the improvements in phase stability and transparency are key factors for the application of this
versatile p-type oxide in transparent electronics and solar cells applications.
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