Quantum confinement in transition metal oxide quantum wells

Abstract

We report on the quantum confinement in SrTiO 3 (STO) quantum wells (QWs) grown by molecular beam epitaxy. The QW structure consists of LaAlO 3 (LAO) and STO layers grown on LAO substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized. Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry in the range of 1.0 eV-6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells. This demonstrates that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material. V

Quantum Confinement in Oxide Heterostructures: Room-Temperature Intersubband Absorption in SrTiO3/LaAlO3 Multiple Quantum Wells

“…This result not only agrees qualitatively with general quantum theory, it also agrees with recent reports on electronic confinement in the STO conduction band of STO/LAO QW heterostructures. 32 We also observe a decrease in absorption peak amplitude that scales with decreasing QW width. This is consistent with a greater population of the ground state in wider wells.…”

“…Notably, our analysis indicates the interfacial roughness is symmetric between the n-and p-type interfaces in our samples, in contrast with many experimental and theoretical reports on STO/LAO heterostructures. 32,34,42 This anomalous 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 6 of 17 feature could be related to the doping in our QWs, as additional charge is required at the n-type interface to avoid the so-called polar catastrophe in LAO. 7,44 Most importantly for the present study, however, both interfaces show remarkably low interfacial roughness, suggesting the observation of intersubband absorption is feasible in our samples.…”

“…31 Unfortunately, in contrast to most perovskite TMO heterostructures, this materials system cannot be integrated directly onto Si (001), limiting its technological significance. Perhaps the most famous of TMO heterostructures, the STO/LAO system boasts a conduction band offset of 2.34 eV, 32 making it a prime candidate for hosting confined electrons. This is to be contrasted with offsets of a meager few tenths of eV in commonly-used GaAs/Ga 1-x Al x As QW heterostructures.…”

Interface‐Induced Polarization in SrTiO3‐LaCrO3 Superlattices

“…Recent work examining LaCoO 3 ‐STO superlattices focused on variation of octahedral tilt angles across the superlattice, but did not indicate any polarization in STO . LaAlO 3 (LAO) and STO superlattice quantum wells have shown unique optical properties due to quantum confinement . LAO‐STO superlattices have also been explored using X‐ray scattering to examine the role of interfacial oxygen vacancies on the electronic structure of STO at the interface .…”

Oxide Materials at the Two-Dimensional Limit

“…However, from a thermodynamic perspective, creation of the heterostructure suggested by Lee et al [181] is somewhat problematic. EuO is not stable under ambient conditions [182], much less the oxygen-rich high-temperature conditions necessary for deposition of crystalline LaAlO3 [183].…”