Effect of Rare Earth Elements at Amorphous ReAlO₃/SrTiO₃ (Re = La, Pr, Nd, Sm, Gd, and Tm) Heterointerfaces

Abstract

Although the amorphous two-dimensional electron gas (a-2DEG) of oxides provides new opportunities to explore nanoelectronic as well as quantum devices, the intrinsic effect of rare earth (Re = La, Pr, Nd, Sm, Gd, and Tm) elements at ReAlO 3 /SrTiO 3 heterointerfaces is still largely unknown and needs to be addressed systematically. Herein, we first propose that the ionization potential of Re elements is a critical factor for the 2DEG fabricated by chemical spin coating. Furthermore, the photoresponsive properties of heterointerfaces are investigated comprehensively with the ionization potential ranging from 35.79 to 41.69 eV. The results show that the sheet resistances significantly increase with increasing the ionization potential, and a resistance upturn phenomenon is observed at TmAlO 3 /SrTiO 3 heterointerfaces, which can be attributed to the weak localization effect theoretically. The most important observation is the dramatic transition from negative (−178.3%, Re = La) to positive (+89.9%, Re = Gd) photoresponse at ReAlO 3 /SrTiO 3 heterointerfaces under the irradiation of 405 nm light at 50 K. More remarkably, a unique recovery behavior of transient−persistent photoconductivity coexistence at low temperatures is discovered at the TmAlO 3 /SrTiO 3 heterointerface. This work reveals an effective approach to tune the transport and photoresponsive properties by changing Re elements and paves the way for the application of all-oxide devices.

Display of Spin–Orbit Coupling at ReAlO3/SrTiO3 (Re = La, Pr, Nd, Sm, and Gd) Heterointerfaces

“…Other detailed results of surface morphology, thickness, and chemical composition of the films have been reported in a previous study. 32 Further, the transport properties of 2DEGs at heterointerfaces are measured. The temperature-dependent sheet resistances (R s ), carrier densities (n s ), and mobilities (μ) of the ReAO/STO heterointerfaces are shown in Figure 2.…”

“…Other ReAO/STO samples prepared under the same preparation conditions have the same morphology and structure. Other detailed results of surface morphology, thickness, and chemical composition of the films have been reported in a previous study …”

Octahedra-Tilted Control of Displacement Disorder and Dielectric Relaxation in Mn-Doped SrTiO3 Single Crystals

“…The cubic unit cell parameter of the STO:Mn single crystal is 3.90663(3) Å. Refinement of the occupancies of the cationic and anionic positions in SrTiO 3 showed that the nearly ideal stoichiometry is observed only in the Sr 2+ sublattice [0.9989 (6)], while the Ti 4+ [0.967(3)] and oxygen [0.988 (9)] sublattices are characterized by the difference from the theoretical values. To determine the position of the Mn cation, during the first stage, we refined the SrTiO 3 structure and built a map of the residual electron density (Figure 1c).…”

“…1,2 It is believed that zero-point quantum fluctuations preclude the condensation of the polar soft mode and a macroscopic ferroelectric state does not form down to the millikelvin range. 1,2 At the same time, the dielectric permittivity reaches ∼10 4 without significant dispersion in the microwave frequency range, 3 which is attractive for application in various types of tunable electronic devices, 4,5 nanotechnology, 6,7 and photocatalysis. 8,9 At ∼105−110 K, STO undergoes an antiferrodistortive transition to a nonferroelectric tetragonal phase formed by out-of-phase tilts of oxygen octahedra.…”

“…Strontium titanate SrTiO 3 (STO) is a perovskite-type material that demonstrates incipient ferroelectric behavior and a quantum paraelectric low-temperature state. , It is believed that zero-point quantum fluctuations preclude the condensation of the polar soft mode and a macroscopic ferroelectric state does not form down to the millikelvin range. , At the same time, the dielectric permittivity reaches ∼10 4 without significant dispersion in the microwave frequency range, which is attractive for application in various types of tunable electronic devices, , nanotechnology, , and photocatalysis. , At ∼105–110 K, STO undergoes an antiferrodistortive transition to a nonferroelectric tetragonal phase formed by out-of-phase tilts of oxygen octahedra. , This improper ferroelastic Pm 3̅ m → I 4/ mcm phase transition has an intermediate nature between second-order and tricritical and is characterized by ultralow values of the order parameter (tilting angle of ∼2° at 1.5 K). , Despite this, the symmetry lowering through the phase transition leads to splitting of the polar soft mode (F 1u ) into two components (E u and A 2u ) and to the appearance of locally polar ferroelastic twin walls , remaining highly mobile down to low temperatures . Moreover, the competition between ferroelectric and antiferrodistortive instabilities (and accompanying strains) can have an even greater impact on the suppression of the polar state than quantum fluctuations. , …”