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Register a new userEffect of Sr-doping of LaMnO3 spacer on modulation-doped two-dimensional electron gases at oxide interfaces
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Modulation-doped oxide two-dimensional electron gas (2DEG) formed at the LaMnO3 (LMO) buffered disorderd-LaAlO3/SrTiO3 (d-LAO/LMO/STO) heterointerface, provides new opportunities for electronics as well as quantum physics. Herein, we studied the dependence of Sr-doping of La1-xSrxMnO3 (LSMO, x=0, 1/8, 1/3, 1/2, and 1) thus the filling of the Mn eg subbands as well as the LSMO polarity on the transport properties of d-LAO/LSMO/STO. Upon increasing the LSMO film thickness from 1 unit cell (uc) to 2 uc, a sharp metal to insulator transition of interface conduction was observed, independent of x. The resultant electron mobility is often higher than 1900 cm2V-1s-1 at 2 K, which increases upon decreasing x. The sheet carrier density, on the other hand, is in the range of 6.9E1012~1.8E1013 cm-2 (0.01~0.03 e/uc) and is largely independent on x for all the metallic d-LAO/LSMO (1 uc)/STO interfaces. These results are consistent with the charge transfer induced modulation doping scheme and clarify that the polarity of the buffer layer plays a trivial role on the modulation doping. The negligible tunability of the carrier density could result from the reduction of LSMO during the deposition of disordered LAO or that the energy levels of Mn 3d electrons at the interface of LSMO/STO are hardly varied even when changing the LSMO composition from LMO to SrMnO3.
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The discovery of two-dimensional electron gases (2DEGs) at the interface between two insulating complex oxides, such as LaAlO3 (LAO) or gamma-Al2O3 (GAO) epitaxially grown on SrTiO3 (STO) 1,2, provides an opportunity for developing all-oxide electronic devices3,4. These 2DEGs at complex oxide interfaces involve many-body interactions and give rise to a rich set of phenomena5, for example, superconductivity6, magnetism7,8, tunable metal-insulator transitions9, and phase separation10. However, large enhancement of the interfacial electron mobility remains a major and long-standing challenge for fundamental as well as applied research of complex oxides11-15. Here, we inserted a single unit cell insulating layer of polar La1-xSrxMnO3 (x=0, 1/8, and 1/3) at the interface between disordered LaAlO3 and crystalline SrTiO3 created at room temperature. We find that the electron mobility of the interfacial 2DEG is enhanced by more than two orders of magnitude. Our in-situ and resonant x-ray spectroscopic in addition to transmission electron microscopy results indicate that the manganite layer undergoes unambiguous electronic reconstruction and leads to modulation doping of such atomically engineered complex oxide heterointerfaces. At low temperatures, the modulation-doped 2DEG exhibits clear Shubnikov-de Haas oscillations and the initial manifestation of the quantum Hall effect, demonstrating an unprecedented high-mobility and low electron density oxide 2DEG system. These findings open new avenues for oxide electronics.
The discovery of two-dimensional electron gas (2DEG) at well-defined interfaces between insulating complex oxides provides the opportunity for a new generation of all-oxide electronics. Particularly, the 2DEG at the interface between two perovskite insulators represented by the formula of ABO3, such as LaAlO3 and SrTiO3, has attracted significant attention. In recent years, progresses have been made to decipher the puzzle of the origin of interface conduction, to design new types of oxide interfaces, and to improve the interfacial carrier mobility significantly. These achievements open the door to explore fundamental as well as applied physics of complex oxides. Here, we review our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures. Due to the presence of oxygen-vacancies at the SrTiO3 surface, metallic conduction can be created at room temperature in perovskite-type interfaces when the overlayer oxide ABO3 involves Al, Ti, Zr, or Hf elements at the B-sites. Furthermore, relying on interface-stabilized oxygen vacancies, we have created a new type of 2DEG at the heterointerface between SrTiO3 and a spinel {gamma}-Al2O3 epitaxial film with compatible oxygen ions sublattices. The spinel/perovskite oxide 2DEG exhibits an electron mobility exceeding 100,000 cm2V-1s-1, more than one order of magnitude higher than those of hitherto investigated perovskite-type interfaces. Our findings pave the way for design of high-mobility all-oxide electronic devices and open a route towards studies of mesoscopic physics with complex oxides.
Well-controlled sub-unit-cell layer-by-layer epitaxial growth of spinel alumina is achieved at room temperature on the TiO2-terminated SrTiO3 single crystalline substrate. By tailoring the interface redox reaction, two-dimensional electron gases with mobilities exceeding 3000 cm2V-1s-1 are achieved at this novel oxide interface.
The predictions of the polar catastrophe scenario to explain the occurrence of a metallic interface in heterostructures of the solid solution(LaAlO$_3$)$_{x}$(SrTiO$_3$)$_{1-x}$ (LASTO:x) grown on (001) SrTiO$_3$ were investigated as a function of film thickness and $x$. The films are insulating for the thinnest layers, but above a critical thickness, $t_c$, the interface exhibits a constant finite conductivity which depends in a predictable manner on $x$. It is shown that $t_c$ scales with the strength of the built-in electric field of the polar material, and is immediately understandable in terms of an electronic reconstruction at the nonpolar-polar interface. These results thus conclusively identify the polar-catastrophe model as the intrinsic origin of the doping at this polar oxide interface.
We report on a systematic investigation of the dominant scattering mechanism in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped GaAs/Al_{x}Ga_{1-x}As heterostructures. The power-law exponent of the electron mobility versus density, mu propto n^{alpha}, is extracted as a function of the 2DEGs depth. When shallower than 130 nm from the surface, the power-law exponent of the 2DEG, as well as the mobility, drops from alpha simeq 1.65 (130 nm deep) to alpha simeq 1.3 (60 nm deep). Our results for shallow 2DEGs are consistent with theoretical expectations for scattering by remote dopants, in contrast to the mobility-limiting background charged impurities of deeper heterostructures.
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