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Origin of Giant Seebeck Coefficient for High Density 2DEGs Confined in the SrTiO3/SrTi0.8Nb0.2O3 Superlattices

Published online by Cambridge University Press:  01 February 2011

Yoriko Mune ,
Hiromichi Ohta ,
Teruyasu Mizoguchi ,
Yuichi Ikuhara  and
Kunihito Koumoto
Yoriko Mune
Affiliation:
[email protected], Nagoya University, Graduated school of engineering, Fro-cho, Chikusa, Nagoya, 464-8603, Japan
Hiromichi Ohta
Affiliation:
[email protected], Nagoya University, Graduated School of Engineering, Fro-cho, Chikusa, Nagoya, 464-8603, Japan
Teruyasu Mizoguchi
Affiliation:
[email protected], The University of Tokyo, Institute of Engineering Innovation, 2-11-16 Yayoi, Bunkyo, Tokyo, 113-8656, Japan
Yuichi Ikuhara
Affiliation:
[email protected], The University of Tokyo, Institute of Engineering Innovation, 2-11-16 Yayoi, Bunkyo, Tokyo, 113-8656, Japan
Kunihito Koumoto
Affiliation:
[email protected], Nagoya University, Graduated School of Engineering, Fro-cho, Chikusa, Nagoya, 464-8603, Japan
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Abstract

Recently, we have found that high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO3 exhibits extremely large Seebeck coefficient (|S|2D) [REF], approximately five times larger than |S|3D. Here we clarify the origin of giant |S|2D using [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]20 (x = 1∼60, y = 1∼20) superlattices. The |S|2D value increased proportionally to y{0.5, indicating that the density of states of the conduction band increases with decreasing y (quantum size effect). Superlattices of [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z (x = 0∼60, y = 1∼20, z = 20) were fabricated on the (001)-face of LaAlO3 substrate by PLD using RHEED to count the number of SrTiO3 or SrTi0.8Nb0.2O3 layers. HR-XRD and HAADF-STEM studies revealed that high-quality [(SrTiO3)17/(SrTi0.8Nb0.2O3)y]z superlattices were successfully fabricated. A dramatic increase of |S|2D is seen with decreasing y-value of the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices. The slope for the plots of log |S|2D - log y is -0.5, and reached 290 μVK−1 (y = 1), which is ∼5 times larger than that of the SrTi0.8Nb0.2O3 bulk (|S|3D = 61 μVK−1). Further, the |S|2D value monotonically increases with x-value and is saturated when x-value > 16 (6.25 nm). We clarified that the critical barrier thickness for electron tunneling in [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattice is 6.25 nm (16 unit cell layers of SrTiO3). The present results give very important information to utilize the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices for practical application.

Keywords

thermoelectricityoxidethin film
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1044: Symposium U – Thermoelectric Power Generation , 2007 , 1044-U09-05
Copyright
Copyright © Materials Research Society 2008

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