Thermoelectric properties of highly conductive p-type CuCrO
2
thin films grown by
metal-organic chemical vapour deposition
P. Lunca Popa, J. Crêpellière, N. Bahlawane, R. Leturcq, D. Lenoble
Material Research and Technology (MRT) Department, Luxembourg Institute of Science and
Technology (LIST), 5 Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg
E-mail :
On the search for a high-mobility p-type transparent oxide semiconductors, Cu-based
delafossite oxides are thought to hold one of the highest potential, and among them CuCrO
2
has already demonstrated high performances in terms of electrical properties and optical vs.
electrical figure of merits. Recently, low-temperature synthesis of highly conductive and
transparent CuCrO
2
with the delafossite crystalline structure has been demonstrated using
metal-organic chemical vapour deposition (MOCVD) [1,2] and spray pyrolysis [3,4], with
figure of merits among the highest for p-type TOS. Although the material is grown without
intentional doping, the observed electrical and thermoelectric properties are comparable to
Mg-doped CuCrO
2
[5]. Moreover they show a strong Cu/Cr non-stoichiometry, obtained in a
wide range of growth parameters [1,2]. These observations question the origin of the doping
in this low temperature grown material, and more generally the influence of Cu, Cr and
related defects in the hole conduction properties of delafossite CuCrO
2
[6].
In order to investigate the origin of the high doping in MOCVD-grown CuCrO
2
, here we
investigate thermoelectric properties of thin films obtained with a large range of synthesis
conditions (temperature, oxygen partial pressure, precursor concentration and fraction, post-
growth annealing). Seebeck coefficient and electrical conductivity have been measured
simultaneously in a temperature range of 140-400 K. The data are directly compared to the
mostly used carrier transport models, such as free electron gas in non-degenerate and
degenerate semiconductor (band conduction) or small polaron hopping. This analysis may
favour the band conduction in our system, with a strongly localized band edge in agreement
with the relatively low carrier mobility of our materials.
[1] J.Crêpellière, P. Lunca-Popa, N. Bahlawane, R. Leturcq, F. Werner, S. Siebentritt, D.
Lenoble,
J. Mater. Chem. C
,
2016
, 4, 4278.
[2] P. Lunca-Popa, J. Crêpellière, R. Leturcq, and D. Lenoble (submitted to thin-solid films).
[3] Farrell, L.; Norton, E.; Smith, C. M.; Caffrey, D.; Shvets, I. & Fleischer, K.
J. Mater.
Chem. C
,
2015
, 4, 126.
[4] Farrell, L.; Fleischer, K.; Caffrey, D.; Mullarkey, D.; Norton, E. & Shvets, I. V.
Phys.
Rev. B
,
2015
, 91, 125202.
[5] Barnabé, A.; Thimont, Y.; Lalanne, M.; Presmanes, L. & Tailhades, P.
J. Mater. Chem. C
,
2015
, 3, 6012-6024.
[6] Norton, E.; Farrell, L.; Callaghan, S. D.; McGuinness, C.; Shvets, I. V. & Fleischer, K.
Phys. Rev. B
,
2016
, 93, 115302.
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