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Strain-induced indirect-to-direct bandgap transition in an np-type LaAlO3/SrTiO3(110) superlattice
1Department of Physics, East China Normal University, No. 500, Dongchuan Road, Shanghai 200241, People's Republic of China. dysun@phy.ecnu.edu.cn.
Abstract:
Using first-principles calculations, we studied the influence of in-plane strain on the electronic properties of the polar LaAlO3/SrTiO3 (LAO/STO)(110) superlattice. We propose that alternate positively (n-type) and negatively (p-type) charged interfaces can be introduced along the [110] direction, without changing the stoichiometry of the system, if the np-type LAO/STO(001) superlattice is constructed in a 45° stepped pattern. We find that when the LAO-STO layer thickness is larger than the critical thickness of the insulator-metal transition, a quasi-two dimensional hole gas and an anisotropic quasi-two dimensional electron gas are formed at alternate interfaces. By applying uniaxial in-plane strains, an unexpected indirect-to-direct bandgap transition occurs in the polar LAO/STO(110) superlattices. The strain-induced changes in the O-2p orbitals near the p-type interface modify the dispersion of valence-band edges, leading to the transition.
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