• Title/Summary/Keyword: Superlattices

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AC Conductivity of $(Sr_{0.75}$,$La_{0.25}$) $TiO_3/SrTiO_3$ Superlattices

  • Choe, Ui-Yeong;Choe, Jae-Du;Lee, Jae-Chan
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2011.05a
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    • pp.31.2-31.2
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    • 2011

  • We have investigated frequency dependant conductivity (or permittivity) of low dimensional oxide structures represented by [($Sr_{0.75}$, $La_{0.25}$)$TiO_3$]$_1$/1$[SrTiO_3]_n$ superlattices. The low dimensional oxide superlattice was made by cumulative stacking of one unit cell thick La doped $SrTiO_3$ and $SrTiO_3$ with variable thickness from 1 to 6 unit cell, i,e, [($Sr_{0.75}$, $La_{0.25}$)$TiO_3$]$_1$/$[SrTiO_3]_n$ (n=1, 2, 3, 4, 5, 6). We found two kinds of relaxation when n is 3 and 4, while, inductance component was observed at n=1. This behavior can be explained by electron modulation in ($Sr_{0.75}$, $La_{0.25}$)$TiO_3/SrTiO_3$ superlattices. When n is 1, electrons by La doping well extend to un-doped layer. Therefore, the transport of superlattices follows bulk-like behavior. On the other hand, as n increased, the doped electrons became two types of carrier: one localized and the other extended. These results in two kinds of transport phase. At further increase of n, most of doped electrons are localized at the doped layer. This result shows that dimensionality of the oxide structure significantly affect the transport of oxide nanostructures.

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The Subband Energy and The Envelope Wave Function of The Semiconductor Superlattice (반도체 초격자의 Subband 에너지와 Envelope 함수)

  • 김영주;손기수
    • Journal of the Korean Vacuum Society
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    • v.1 no.1
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    • pp.60-66
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    • 1992

  • The electronic subband structure and the envelope wave function for three types of superlattices are calculated with a new method. Comparison of the results of this method with those of other methods has proved the validity of this method. In particullas, the results of saw-toothed superlattices show that the change of the effective mass with position must be considered. Therefore this method can be easily applied to arbitrily shaped superlattices and multiple quantum well structures.

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Structural Stability and the Electronic Structure of InP/GaP Superlattices

  • Park, Cheol-Hong;Chang, Kee-Joo
    • ETRI Journal
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    • v.13 no.4
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    • pp.25-34
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    • 1991

  • The stability and the electronic structure of $In_0.5$.$Ga_0.5$P-based superlattices are examined through self-consistent ab initio pseudopotential calculations. A chalcopyrite-like structure is found to be the lowest energy state over (001) and (111) monolayer superlattices (MLS). Our calculations indicate that all the ordered structures in bulk form are unstable against phase segregation into binary constituents at T = 0 while for epitaxial growth, the chalcopyrite phase is stabilized. The fundamental band gaps of the ordered structures are found to be direct and smaller than that of disordered alloys. The lowering of the band gap is explainable by band folding and pushing effects. We find the reduction of the band gap to be largest for the (111) MLS.

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Analysis on Thermal Boundary Resistance at the Interfaces in Superlattices by Using the Molecular Dynamics (분자동역학법을 이용한 초격자 내부의 경계면 열저항의 해석)

  • Choi, Soon-Ho;lee, Jung-Hye;Choi, Hyun-Kue;Yoon, Seok-Hun;Oh, Cheol;Kim, Myoung-Hwan
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1382-1387
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    • 2004

  • From the viewpoint of a macro state, there is no thermal boundary resistance (TBR) at an interface if both surfaces at an interface are perfectly contacted. However, recent molecular dynamics (MD) studies reported that there still exists the TDR at the interface in an ideal epitaxial superlttice. Our previous studies suggested the model to predict the TBR not only quantitatively also qualitatively in superlattices. The suggested model was based on the classical theory of a wave reflection, and provided highly satisfactory results for an engineering purpose. However, it was not the complete model because our previous model was derived by considering only the effects from a mass ratio and a potential ratio of two species. The interaction of two species presented by the Lennard-Jones (L-J) potential is governed by the mutual ratio of the masses, the potential well depths, and the diameters. In this study, we performed the preliminary simulations to investigate the effect resulting from the diameter ratio of two species for the completion of our model and confirmed that it was also a ruling factor to the TBR at an interface in superlattices.

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