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Bi2Te3 is attracting a renewed interest due to its topological insulator properties; however, even using advanced physical and chemical deposition techniques, the growth of high crystal quality layers on substrates allowing its technological employment, such as Si, is very challenging due to the structural complexity of Bi2Te3. In this work, we present the optimized large-area growth of topological insulator Bi2Te3 epitaxial layers on unbuffered i-Si(111) substrates via metal-organic vapor phase epitaxy (MOVPE), which is of crucial importance for future integration into CMOS-compatible spintronic devices. We found that the key to maximizing the layer quality requires a balanced control of the reactor pressure (P), growth temperature (T), and growth time (t). Within a proper parameter window, the grown Bi2Te3 thin layers are crystalline, stoichiometric, and highly uniform, also at the local scale. They exhibit a rhombohedral crystalline structure, and they are [001] out-of-plane oriented on the i-Si(111) substrate. Low-temperature magnetoresistance measurements revealed clear weak antilocalization effects, demonstrating that the optimized MOVPE-grown Bi2Te3 is a topological insulator, hence opening further possibilities for its technology transfer to innovative devices.

Antimony telluride (Sb2Te3) thin films were obtained by metalorganic chemical vapor deposition (MOCVD). The films were grown on crystalline Si(100) and Al2O3(0001) and amorphous SiO2 and a-Al2O3 substrates. Their structural properties were compared with those of the Sb2Te3/Si(111) heterostructure. In addition to the effect of the substrate, the influence of pre- and post-growth thermal annealing is also presented. The quality of the films is discussed by comparing their morphological properties, such as roughness and granularity, and ascertaining their crystallinity and their in-plane and out-of-plane orientation.

Antimony telluride (Sb2Te3) thin films were prepared by a room temperature Metal-Organic Chemical Vapor Deposition (MOCVD) process using antimony chloride (SbCl3) and bis(trimethylsilyl)telluride (Te(SiMe3)2) as precursors. Pre-growth and post-growth treatments were found to be pivotal in favoring out-of-plane and in-plane alignment of the crystallites composing the films. A comprehensive suite of characterization techniques were used to evaluate their composition, surface roughness, as well as to assess their morphology, crystallinity, and structural features, revealing that a quick post-growth annealing triggers the formation of epitaxial-quality Sb2Te3films on Si(111).

Interfacing topological insulators (TI) with ferromagnetic (FM) layers is a promising route towards the next generation of ultra-low power spintronic devices based on charge-to-spin current conversion. Here, we present the Fe/Sb2Te3 interface structure, its chemical composition and magnetic properties. Thin films (30 nm) of the topological insulator Sb2Te3 were synthesized by Metal Organic Chemical Vapor Deposition (MOCVD) at room temperature on Si/SiO2 substrates, then capped with a 54Fe(10 nm)/57Fe(1 nm) bilayer by Pulsed Laser Deposition (PLD) to allow interface-sensitive Conversion Electron Mössbauer Spectroscopy (CEMS). X-ray diffraction (XRD) showed the polycrystalline nature of both the Fe and Sb2Te3 layers. X-ray reflectivity (XRR) identified a non-trivial layered structure with the presence of an intermixed layer at the Fe/Sb2Te3 interface. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) confirmed the partial elemental interdiffusion between the Fe and Sb2Te3 layers. Interface-sensitive CEMS evidenced that about a half of the 1-nm-thick 57Fe layer in contact with Sb2Te3 coordinates ferromagnetically, whereas the remaining paramagnetic fraction preferentially bonds with Te. The Fe/Sb2Te3 system was shown to have a far from sharp interface, exhibiting a marked chemical reactivity already at room temperature. The tendency of Fe to preferentially bond with the chalcogenide element of topological insulators has been previously observed for the interface with Bi2Se3 and Bi2Te3, thus suggesting a possible universal behavior at the interface between Fe and chalcogenide-based TI.

When coupled with ferromagnetic layers (FM), topological insulators (TI) are expected to boost the charge‐to‐spin conversion efficiency across the FM/TI interface. In this context, a thorough control and optimization of the FM/TI interface quality are requested. Here, the evolution of the chemical, structural, and magnetic properties of the Fe/Sb2Te3 heterostructure is presented as a function of a rapid mild thermal annealing conducted on the Sb2Te3‐TI (up to 200 °C). While the bilayer is not subjected to any thermal treatment upon Fe deposition, the annealing of Sb2Te3 markedly improves its crystalline quality, leading to an increase in the fraction of ferromagnetic Fe atoms at the buried Fe/Sb2Te3 interface and a slight lowering of the magnetic coercivity of the Fe layer. The method is an efficient tool to clean up the Fe/Sb2Te3 interface, which may be extended to different FM/TI heterostructures. Simultaneously to the interface reconstruction, a constant ≈20% fraction of FeTe develops at the interface. Since FeTe can display superconductivity, the Fe/Sb2Te3 system could have potentialities for exploiting phenomena at the edge of magnetism, superconductivity and topology.

Taking the full advantage of the conformal growth characterizing atomic layer deposition (ALD), the possibility to grow Co thin films, with thickness from several tens down to few nanometers on top of a granular topological insulator (TI) Sb2Te3 film, exhibiting a quite high surface roughness (2–5 nm), was demonstrated. To study the Co growth on the Sb2Te3 substrate, we performed simultaneous Co depositions also on sputtered Pt substrates for comparison. We conducted a thorough chemical-structural characterization of the Co/Sb2Te3 and Co/Pt heterostructures, confirming for both cases, not only an excellent conformality, but also the structural continuity of the Co layers. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the [00l] direction, following the underlying rhombohedric substrate. Differently, Co crystallizes in a cubic phase oriented along the [111] direction when deposited on Pt. This work shows that, in case of deposition of crystalline materials, the ALD surface selectivity and conformality can be extended to the definition of local epitaxy, where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate. Moreover, a highly sharp and chemically-pure Co/Sb2Te3 interface was evidenced, which is promising for the application of this growth process for spintronics. [Figure not available: see fulltext.].