Enhanced persistent photoconductivity in $\delta$-doped LaAlO${}_3$/SrTiO${}_3$ heterostructures

Abstract

We report the effect of $\delta$-doping at LaAlO${}_3$/SrTiO${}_3$ interface with LaMnO${}_3$ monolayers on the photoconducting (PC) state. The PC is realized by exposing the samples to broad band optical radiation of a quartz lamp and 325 and 441 nm lines of a He-Cd laser. Along with the significant modification in electrical transport which drives the pure LaAlO${}_3$/SrTiO${}_3$ interface from metal-to-insulator with increasing LaMnO${}_3$ sub-monolayer thickness, we also observe an enhancement in the photo-response and relaxation time constant. Possible scenario for the PC based on defect-clusters, random potential fluctuations and large lattice relaxation models have been discussed. For pure LaAlO${}_3$/SrTiO${}_3$, the photoconductivity appears to originate from inter-band transitions between Ti-derived $3d$ bands which are $e_g$ in character and O 2p - Ti $t_{2g}$ hybridized bands. The band structure changes significantly when fractional layers of LaMnO${}_3$ are introduced. Here the Mn $e_g$ bands ($\approx 1.5$ eV above the Fermi energy) within the photo-conducting gap lead to a reduction in the photo-excitation energy and a gain in overall photoconductivity.

9 pages, 5 figures

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• Electric Field Control of the LaAlO${}_3$/SrTiO${}_3$ Interface Ground State
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Cited by in corpus (3)

• Photoresponse dynamics in amorphous-LaAlO${}_3$/SrTiO${}_3$ interfaces
• Dynamics of photo-generated non-equilibrium electronic states in Ar${}^{+}$ ion irradiated SrTiO${}_3$
• Towards Mott design by $\delta$-doping of strongly correlated titanates