![]() We determine the in-plane crystalline orientation of SnTe(001) by measuring ϕ-rocking curves at the SnTe (2 0 6) and SrTiO 3 (1 0 6) Bragg reflections. Because the SnTe film consists only of (0 0 1) oriented crystals, the film is terminated with a (0 0 1) plane at the SrTiO 3 interface, which consists of both Sn and Te atoms. Specular diffraction measurements reveal (0 0 1) SnTe fully relaxed from the SrTiO 3 lattice. We target a Ψ corresponding to a greater thickness than desired because the SnTe continues to evaporate while the sample is cooled.įollowing growth of SnTe(001) thin films by coSubDep, we characterize the SnTe crystalline orientation by measuring x-ray diffraction. To achieve films of 10–20 u.c., we target Ψ = 15, which corresponds to a thickness of ∼25 u.c. A plot of these values over deposition of 200 u.c. 1(a), the value of Ψ is a particularly sensitive measure of thickness from 0 to 75 u.c. 27 An accurate calibration of the ellipsometry insensitive to geometrical details such as the sample position and orientation of the polarizers is performed by measuring the values of ∆ and Ψ with respect to the thickness determined by a quartz crystal monitor. Two values parameterizing the shift in polarization upon reflection, ∆ and Ψ, are measured and are sufficient to characterize the thickness using known values of the complex index of refraction for SnTe. 27 The laser, polarizer, and analyzer are mounted to the windows of the growth chamber, with a specular reflection angle of ∼40° with respect to the sample normal. This method is sensitive to film thickness at small values due to the high absorption coefficient of SnTe at the wavelength of the helium–neon laser (632 nm). Ellipsometry allows us to reproducibly stop evaporation at the desired thickness. 25 Here, we utilize laser ellipsometry to track the sublimation step of coSubDep in real time. Previously, multiple trials with different evaporation times were used to achieve films with the desired thickness. We deposit thick SnTe films (>150 u.c.) by conventional molecular beam epitaxy and then elevate the substrate temperature under constant SnTe flux until we reach a net negative growth rate of the film thickness. 26Īs described previously, 25 coSubDep is used to achieve continuous SnTe films with single (001) orientation. 25 With its high dielectric constant and large bandgap, SrTiO 3 is a promising substrate for gated-SnTe, with SrTiO 3 serving as an insulating buffer layer between SnTe and a conducting oxide gate. on SrTiO 3 with higher continuity and crystalline uniformity. A modified molecular beam epitaxy technique called co-sublimation-deposition (coSubDep) has been shown to produce SnTe films as thin as 10 u.c. Yet, on substrates both with and without close lattice matches, SnTe forms discontinuous films with multiple crystalline orientations, not suitable for gate-controlled devices. 17–23 Techniques such as molecular beam epitaxy and chemical vapor deposition have been favored over exfoliation, commonly used for other 2D materials, 24 because of the strong interlayer bonds in SnTe. The maximum phase coherence length is achieved for films thicker than 20 unit cells, which could be used for gated-SnTe devices.Īngle-resolved photoelectron spectroscopy and scanning tunneling microscopy 9–18 have identified topological surface states in flakes and discontinuous films of SnTe however, synthesizing SnTe films with uniform crystalline orientation and continuity to engineer devices has proven difficult. This method of analysis may be suitable to analyze the magnetotransport characteristics of any topological material with carriers in both topological and trivial bulk states. Magnetoconductivity measurements of SnTe films reveal a coexistence of weak antilocalization, consistent with topologically non-trivial states, and weak localization, consistent with trivial states from the bulk. Continuous, single-phase SnTe films with a (001) orientation relative to the SrTiO 3 lattice are achieved. This process takes advantage of a thin SnTe template layer crystallized after amorphous deposition, with additional SnTe being grown by molecular beam epitaxy and monitored with in situ laser ellipsometry. Here, we present an optimized templating procedure for depositing single-orientation, continuous films of TCI SnTe on SrTiO 3, which is an oxide with a wide bandgap and large dielectric constant suitable for gated devices. ![]() To realize TCI devices with gate-controlled topological states, it is necessary to develop methods for depositing continuous and thin TCI films on substrates suitable for electric-field gating. Topological crystalline insulators (TCIs) promise spin-polarized or dissipationless transport, which can be controlled by crystal symmetry breaking through applied strain or electric field. ![]()
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