The Effect of Polar Fluctuation and Lattice Mismatch on Carrier Mobility at Oxide Interfaces

Abstract

Since the discovery of two-dimensional electron gas (2DEG) at the oxide interface of LaAlOinterface. The minimal thickness of the polar layer t C that is required for electronic reconstruction is t C =  0  P E/eP, where  P is the dielectric constant of the polar material, E is the energy gap separating the valance band of the polar layer and the conduction band of the nonpolar material, and P is the electric polarization of polar layers [10]. Taking  P = 24, E as STO bandgap of 3.2 eV, and P = 0.526 C m -2 for the LAO/STO (001) interface, t C is calculated to be 4 unit cells (uc) Here we show that this can be accomplished by replacing LAO with LSAT - When grown on STO, the lattice mismatch for LSAT/STO is only 1.0%, which is only one third of the value of LAO/STO (3.0%). Furthermore, STO and LSAT both undergo a similar cubic-to-tetragonal transition below 100 K [25,26], whereby maintaining the structural coherency. Fig. 1(c).Given the nonpolar nature of SrTiO 3 (001), a polar-discontinuity-induced 2DEG is expected at the LSAT/STO (001) interface.The thickness-dependent transport data at 2 K for the LSAT/STO (001), (110), and (111) interfaces are summarized in Figs. 2(a)-2(c), respectively. In Fig. 2(a), the (001) interface becomes conducting when covered by a LSAT layer with thickness t ≥ 5 uc. Furthermore, the low-temperature sheet conductance of LSAT/STO increasers with t, reaching its highest value at t ≈ 12 uc. This conductance improvement is not caused by any increases of carrier density, but it is brought about by a great enhancement of carrier mobility  S , which reaches its peak of 35,000 cm 2 V -1 s -1 at t = 12 uc.And this high carrier mobility is about 30 times larger than that of LAO/STO interfaces prepared under similar conditions [5,21,22]. Also, we note that clear Shubnikov-de Haas conductance oscillations can be observed at 2 K for (001) interfaces with high carrier mobility (Fig. S3 in Supplementary Materials [30]). In addition, the transport data clearly show that there are two critical thicknesses for the LSAT/STO (001) interface: one is at 5 uc where the 2DEG is established and the other is around 12 uc where the mobility is greatest.On the other hand, this high mobility 2DEG is also observed at the annealed (110)-and (111)-orientated LSAT/STO interfaces, which is similar to the LAO/STO interface with different orientations [22,31]. But unlike LSAT/STO (001) interface, both the (110) and (111) (110) and (111) LSAT/STO interfaces show much more robust metallicity. For example, our data show that the high-mobility 2DEG can be maintained in the LSAT/STO (110) and (111) interfaces with a 50-uc-thick LSAT layer, while the LAO/STO (110) and (111) interfaces show low-temperature insulating behavior when LAO thickness is beyond just 10 uc [22].Therefore, two major differences between LSAT/STO and LAO/STO interfaces can be found in Fig. 2. One is the much higher carrier mobility and more robust metallicity at the LSAT/STO interface, and the other one is the observation of two critical th...

Strong spin-orbit coupling and magnetism in (111) (La0.3Sr0.7)(Al0.65Ta0.35Bal1, Huang2, Han3 et al. 2018Phys. Rev. BSelf Cite4290View full textAdd to dashboardCite

“…30 Here we report studies of the MR of LSAT deposited epitaxially on (111) STO. LSAT has a 1% lattice mismatch with STO, as opposed to a 3% mismatch in the case of LAO/STO, 31 which leads to a comparatively lower strain. As with the (001) LAO/STO heterostructures, we find that the SOI can be tuned by V g .…”

“…The sample had 12 monolayers of LSAT deposited on (111) oriented STO using pulsed laser deposition, at a growth partial oxygen pressure of 10 −4 Torr. 31,32 No post growth annealing step was performed. Ti/Au was deposited on contact pads of the Hall bars, and Al wirebonds were made to allow for a 4-probe measurement of transverse and longitudinal resistance.…”

Electrostatic tuning of magnetism at the conducting (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 interface

“…Earlier work on (001) LAO/STO interfaces 15 demonstrated that strain at the interface can drastically change conduction, whereas recent studies of LSAT grown on (001) STO suggested that the lower strain compared to LAO significantly increased the carrier mobility. 24,29 However, there have been only a few transport experiments performed on LSAT/STO interfaces to date, and none on (111) oriented LSAT/STO. In particular, the effect of an electric field, which has proved to be a powerful tool to probe the properties of other STO based interface devices, has not been studied in the case of LSAT/STO.…”

δ‐Doping Effects on Electronic and Energetic Properties of LaAlO3/SrTiO3 Heterostructure: First‐Principles Analysis of 23 Transition‐Metal Dopants

“…Actually, a small lattice mismatch between the film and the substrate is expected to improve the crystalline quality of the heterointerface, thus increases the scattering time and accordingly electron mobility, which is extremely difficult to accurately quantify from first‐principles calculations, though. For example, very recently, Ariando and co‐workers have reported that by replacing LaAlO 3 with cubic (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )O 3 (LSAT), the lattice mismatch between the film and the SrTiO 3 substrate is reduced from 3.0% to 1.0%, and interfacial electron mobility can be significantly improved (about 35 000 cm 2 V −1 s −1 at 2 K), which is almost 30 times larger than that in the conventional LaAlO 3 /SrTiO 3 . One the other hand, Gunkel et al proposed that the reduced epitaxial strain in LSAT/SrTiO 3 has only minor effects on the improved mobility.…”