Controlled growth of complex polar oxide films with atomically precise molecular beam epitaxy

Abstract

At heterointerfaces between complex oxides with polar discontinuity, the instability-induced electric field may drive electron redistribution, causing a dramatic change in the interfacial charge density. This results in the emergence of a rich diversity of exotic physical phenomena in these quasi-two-dimensional systems, which can be further tuned by an external field. To develop novel multifunctional electronic devices, it is essential to control the growth of polar oxide films and heterointerfaces with atomic precision. In this article, we review recent progress in control techniques for oxide film growth by molecular beam epitaxy (MBE). We emphasize the importance of tuning the microscopic surface structures of polar films for developing precise growth control techniques. Taking the polar SrTiO3 (110) and (111) surfaces as examples, we show that, by keeping the surface reconstructed throughout MBE growth, high-quality layer-by-layer homoepitaxy can be realized. Because the stability of different reconstructions is determined by the surface cation concentration, the growth rate from the Sr/Ti evaporation source can be monitored in real time. A precise, automated control method is established by which insulating homoepitaxial SrTiO3 (110) and (111) films can be obtained on doped metallic substrates. The films show atomically well-defined surfaces and high dielectric performance, which allows the surface carrier concentration to be tuned in the range of ~1013/cm2. By applying the knowledge of microstructures from fundamental surface physics to film growth techniques, new opportunities are provided for material science and related research.