Volume 113, Number 4, February 2016
|Number of page(s)||6|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||14 March 2016|
Infrared ellipsometry study of the confined electrons in a high-mobility γ-Al2O3/SrTiO3 heterostructure
1 University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials Chemin du Musée 3, CH-1700 Fribourg, Switzerland
2 Department of Condensed Matter Physics, Faculty of Science and Central European Institute of Technology, Masaryk University - Kotlářska 2, 61137 Brno, Czech Republic
3 Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus 4000 Roskilde, Denmark
Received: 17 February 2016
Accepted: 3 March 2016
With infrared ellipsometry we studied the response of the confined electrons in γ-Al2O3/SrTiO3 (GAO/STO) heterostructures in which they originate predominantly from oxygen vacancies. From the analysis of a so-called Berreman mode, that develops near the highest longitudinal optical phonon mode of SrTiO3, we derive the sheet carrier density, Ns, the mobility, μ, and the depth profile of the carrier concentration. Notably, we find that Ns and the shape of the depth profile are similar as in LaAlO3/SrTiO3 (LAO/STO) heterostructures for which the itinerant carriers are believed to arise from a polar discontinuity. Despite an order of magnitude higher mobility in GAO/STO, as obtained from transport measurements, the derived mobility in the infrared range exhibits only a twofold increase. We interpret this finding in terms of the polaronic nature of the confined charge carriers in GAO/STO and LAO/STO which leads to a strong, frequency-dependent interaction with the STO phonons.
PACS: 78.20.-e – Optical properties of bulk materials and thin films / 78.67.-n – Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures / 78.30.-j – Infrared and Raman spectra
© EPLA, 2016
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