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Transparent conducting oxides: a δ-doped superlattice approach.

Cooper VR, Seo SS, Lee S, Kim JS, Choi WS, Okamoto S, Lee HN - Sci Rep (2014)

Bottom Line: We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d states.In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of quantum mechanical wavefunctions between neighboring δ-doped layers.These results highlight the potential for using oxide heterostructures in optoelectronic devices by providing a unique route for creating novel transparent conducting oxides.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

ABSTRACT
Metallic states appearing at interfaces between dissimilar insulating oxides exhibit intriguing phenomena such as superconductivity and magnetism. Despite tremendous progress in understanding their origins, very little is known about how to control the conduction pathways and the distribution of charge carriers. Using optical spectroscopic measurements and density-functional theory (DFT) simulations, we examine the effect of SrTiO3 (STO) spacer layer thickness on the optical transparency and carrier distribution in La δ-doped STO superlattices. We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d states. In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of quantum mechanical wavefunctions between neighboring δ-doped layers. These results highlight the potential for using oxide heterostructures in optoelectronic devices by providing a unique route for creating novel transparent conducting oxides.

No MeSH data available.


DOS calculated for undoped STO, O-deficient SrTiO2.875, [L1/S2], and [L1/S6].The solid lines and shaded areas represent the total DOS and projected DOS for Ti 3d-states, respectively.
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f2: DOS calculated for undoped STO, O-deficient SrTiO2.875, [L1/S2], and [L1/S6].The solid lines and shaded areas represent the total DOS and projected DOS for Ti 3d-states, respectively.

Mentions: As evident from the density of states (DOS) shown in Figure 2, δ-doped superlattices have their Fermi levels residing within the Ti bands and the gap between the O 2p states and Ti 3d-t2g states (the allowed optical transition) remains, relatively, the same as in undoped STO. As such, these materials should be transparent to visible light. (N.B.: Our DFT calculations underestimate the band gap; thus, even though they are smaller than the required 3 eV, the results are consistent with a material that would be optically transparent). This is unlike the O-deficient SrTiO2.875, where bulk dopants result in the narrowing of the band gap through the creation of in-gap states (see Figure 2 and 3b). Additionally, analysis of the band structure (Figure 3c and d) shows that the transitions from the conduction states to higher lying unoccupied 3d-states are ~2 eV or less, consistent with the Drude feature observed experimentally (Figure 1a).


Transparent conducting oxides: a δ-doped superlattice approach.

Cooper VR, Seo SS, Lee S, Kim JS, Choi WS, Okamoto S, Lee HN - Sci Rep (2014)

DOS calculated for undoped STO, O-deficient SrTiO2.875, [L1/S2], and [L1/S6].The solid lines and shaded areas represent the total DOS and projected DOS for Ti 3d-states, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4127498&req=5

f2: DOS calculated for undoped STO, O-deficient SrTiO2.875, [L1/S2], and [L1/S6].The solid lines and shaded areas represent the total DOS and projected DOS for Ti 3d-states, respectively.
Mentions: As evident from the density of states (DOS) shown in Figure 2, δ-doped superlattices have their Fermi levels residing within the Ti bands and the gap between the O 2p states and Ti 3d-t2g states (the allowed optical transition) remains, relatively, the same as in undoped STO. As such, these materials should be transparent to visible light. (N.B.: Our DFT calculations underestimate the band gap; thus, even though they are smaller than the required 3 eV, the results are consistent with a material that would be optically transparent). This is unlike the O-deficient SrTiO2.875, where bulk dopants result in the narrowing of the band gap through the creation of in-gap states (see Figure 2 and 3b). Additionally, analysis of the band structure (Figure 3c and d) shows that the transitions from the conduction states to higher lying unoccupied 3d-states are ~2 eV or less, consistent with the Drude feature observed experimentally (Figure 1a).

Bottom Line: We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d states.In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of quantum mechanical wavefunctions between neighboring δ-doped layers.These results highlight the potential for using oxide heterostructures in optoelectronic devices by providing a unique route for creating novel transparent conducting oxides.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

ABSTRACT
Metallic states appearing at interfaces between dissimilar insulating oxides exhibit intriguing phenomena such as superconductivity and magnetism. Despite tremendous progress in understanding their origins, very little is known about how to control the conduction pathways and the distribution of charge carriers. Using optical spectroscopic measurements and density-functional theory (DFT) simulations, we examine the effect of SrTiO3 (STO) spacer layer thickness on the optical transparency and carrier distribution in La δ-doped STO superlattices. We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d states. In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of quantum mechanical wavefunctions between neighboring δ-doped layers. These results highlight the potential for using oxide heterostructures in optoelectronic devices by providing a unique route for creating novel transparent conducting oxides.

No MeSH data available.