Recently, high mobile electrons have been found in the heterostructure made of two insulators, lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3 ). This interesting conducting behavior at the heterointerface of insulators has attracted a number of research activities to understand the origin of carriers. However, the origin of carriers and the conducting mechanisms are not well understood and still under debate. In this study, in order to understand the fundamental physics of the conducting LaAlO3/SrTiO3 heterointerfaces, atomic scale simulations and continuum modeling have been performed for various types of heterostructures.
First, the heterostructures are analyzed by ab-initio calculations using Density Functional Theory (DFT) calculations to find the most stable structures. It has been found that the heterostructures with atomic diffusions are more stable than one without diffusion. As the thickness of LaAlO3 film increases, the types of diffused atoms changes from B-site atomic diffusion to B-site atomic diffusions. From these DFT calculations, important electrical properties such as effective electron and hole masses have been obtained. Second, electron transport properties have been investigated using quantum mechanical approaches. Carrier distributions and band structures for heterostructures with and without atomic-diffusions are calculated by solving Schrödinger equations self-consistently with Poisson equation. The calculated sheet densities as a function of LaAlO3 film thickness indicate that the heterostructure with La atom exchanging with Sr atom has the critical thickness of 4 unit cells (u.c.) consistent with other experimental observations. It is found that the interface remains non-conducting up to 3 u.c. of LaAlO3 film and becomes conducting for the film thicker than 3 u.c. Using the energy levels and wavefunctions from the self-consistent calculations, the electron mobility has been calculated from the linearized Boltzmann equation including various scattering mechanisms, such as acoustic phonon, polar optical phonon, impurity, and interface roughness. At low temperature, the mobility is limited by impurity and interface roughness scattering. At high temperature, the polar optical phonon is the dominant scattering center.
|Advisor:||You, Jeong Ho|
|Commitee:||Chen, Jinghong, Tong, Wei|
|School:||Southern Methodist University|
|School Location:||United States -- Texas|
|Source:||MAI 51/03M(E), Masters Abstracts International|
|Subjects:||Mechanical engineering, Materials science|
|Keywords:||Density functional theory, Heterostructure, Self-consistent calculation|
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