Buffer-layer-controlled Nickeline vs Zinc-Blende/Wurtzite-type MnTe growths on c-plane Al2O3 substrates
arxiv(2024)
Abstract
In the recent past, MnTe has proven to be a crucial component of the
intrinsic magnetic topological insulator (IMTI) family [MnTe]m[Bi2Te3]n, which
hosts a wide range of magneto-topological properties depending on the choice of
m and n. However, bulk crystal growth allows only a few combinations of m and n
for these IMTIs due to the strict limitations of the thermodynamic growth
conditions. One way to overcome this challenge is to utilize atomic
layer-by-layer molecular beam epitaxy (MBE) technique, which allows arbitrary
sequences of [MnTe]m and [Bi2Te3]n to be formed beyond the thermodynamic limit.
For such MBE growth, finding optimal growth templates and conditions for the
parent building block, MnTe, is a key requirement. Here, we report that two
different hexagonal phases of MnTe-nickeline (NC) and zinc-blende/wurtzite
(ZB-WZ) structures, with distinct in-plane lattice constants of 4.20 +/- 0.04 A
and 4.39 +/- 0.04 A, respectively-can be selectively grown on c-plane Al2O3
substrates using different buffer layers and growth temperatures. Moreover, we
provide the first comparative studies of different MnTe phases using
atomic-resolution scanning transmission electron microscopy and show that ZB
and WZ-like stacking sequences can easily alternate between the two.
Surprisingly, In2Se3 buffer layer, despite its lattice constant (4.02 A) being
closer to that of the NC phase, fosters the ZB-WZ instead, whereas Bi2Te3,
sharing the same lattice constant (4.39 A) with the ZB-WZ phase, fosters the NC
phase. These discoveries suggest that lattice matching is not always the most
critical factor determining the preferred phase during epitaxial growth.
Overall, this will deepen our understanding of epitaxial growth modes for
chalcogenide materials and accelerate progress toward new IMTI phases as well
as other magneto-topological applications.
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