Low-Temperature Epitaxial Growth of Anti-Ferromagnetic MnTe at Bi₂Te₃

There is significant scientific and technological interest in the epitaxial integration of ferromagnetic or antiferromagnetic materials with the topological insulators (TI). This allows the introduction of the ferromagnetic order into a topological insulator system and may lead to the development of novel spin electronic devices. It is anticipated that these heterostructures can be used as novel magnetoresistive random access memory (MRAM) devices with high charge-to-spin conversion efficiency. This implies that TI-based heterostructures can switch between 0 and 1 memory states much more efficiently, while consuming lower energy than the state-of-the-art magnetic tunneling junction-based heterostructures that use transition metals. The TI-based devices will be less susceptive to weak disorder and perturbations since writing process will occur via conventional writing field while electrical read out process will be topologically protected.<br/> A key requirement for an operational heterojunction is a successful coupling of a TI with the magnetic material, which is facilitated by “atomically-clean” and abrupt junction interface. This should involve low-temperature deposition of the magnetic layer on the TI surface. This eliminates usage of the standard magnetic materials growth techniques, such as molecular beam epitaxy (MBE) and pulsed laser deposition, as they require the substrate temperatures greater than 300-350 ⁰C, above what TIs can survive.<br/> Here, we report on the innovative approach to grow a room-temperature antiferromagnetic semiconductor (MnTe) using atomic layer deposition (ALD) and to epitaxially integrate it with the topological insulator (Bi₂Te₃). MnTe films were deposited at &lt;100&gt; GaAs and &lt;111&gt; InP. While the MnTe at &lt;100&gt; GaAs were polycrystalline, epitaxial growth was achieved at closely lattice-matched &lt;111&gt; InP at temperatures as low as 120 ⁰C. Bi₂Te₃ was grown by MBE at c-Al₂O₃, <i>ex-situ</i> transferred into the ALD system, and used as a template for MnTe growth. High-resolution X-ray diffraction studies demonstrated that epitaxial MnTe growth was achieved at 120 ⁰C. Transmission electron microscopy showed that the MnTe / Bi₂Te₃ interface was atomically sharp. No amorphous and / or disordered regions were present at the interface within the imaged regions. Magnetotransport properties of the ALD-grown MnTe were also studied and will be reported here.<br/> In summary, ALD was successfully used for the low-temperature epitaxial integration of MnTe antiferromagnetic semiconductor with the Bi₂Te₃ topological insulator. This opens the path for the realization of near-room temperature energy-efficient spintronic devices.