Vapor phase growth and characterization of van der Waals BiSbTeSe platelets on semiconducting MoS2
Three dimensional topological insulators of the tetradymite family, such as BiSbTeSe (BSTS), are attractive for spintronic and quantum device applications because of their compensated, bulk-insulating character. Nanostructured BSTS platelets are promising for practical TI based devices. However, their growth often requires complex equipment, organometallic precursors, or electrically insulating substrates. Simple growth on technologically relevant semiconducting substrates remains largely unexplored. Here, we report the vapor phase growth of van der Waals BSTS platelets directly on semiconducting MoS2 using a presynthesized BiSbTe1.5Se1.5 crystal as the source material. The grown BSTS platelets exhibit thicknesses ranging from 4 nm to 246 nm, with an average lateral size of 1.4 mkm for individual platelets. Raman spectra of platelets, acquired in correlation with AFM thickness measurements, reveal contributions from both BSTS and the underlying MoS2 substrate. Among the characteristic BSTS modes, A21g mode shows the highest sensitivity to platelet thickness and local composition. EDS analysis reveals a systematic thickness dependence of the platelet composition, with an apparent crossover around 49 nm that coincides with a change in the thickness dependence of the low-wavenumber component of the E2g Raman band. This correlation suggests a composition-related origin of the Raman behavior, with the compositional variations tentatively attributed to the differential volatility of the constituent elements during growth. These results demonstrate that MoS2 is a promising van der Waals platform for BSTS deposition and provide a structural and compositional baseline for future studies of BSTS-MoS2 heterostructures.