Strong (110) Texturing and Heteroepitaxial Growth of Thin Mo Films on MoS₂ Monolayer

Growth of textured and low-resistivity metallic seed layers for AlN-based piezoelectric films is of high importance for bulk acoustic wave resonator applications. Through optimization of Mo physical vapor deposition parameters, namely, the Ar flow rate, strong (110) texturing and low electrical resistivities (∼3 × 10–7 Ω m) were observed for 43 ± 3 nm thick Mo films on a CVD-grown MoS2 monolayer on c-Al2O3(0001) substrates. The strong texturing was attributed to the growth template effect of the monolayer MoS2 due to the presence of a local epitaxial relationship between (110)-Mo and (0001)-MoS2 (i.e., through MoS2(0001)[112̅0]||Mo(110)[1̅11] and/or MoS2(0001)[112̅0]||Mo(110)[001]), coupled with an atomic-scale flatness of the MoS2 surface, which promotes layer-by-layer growth of the Mo film. The deposited Mo/MoS2 monolayer stack can also be easily peeled-off from the growth Al2O3(0001) substrate for possible subsequent transfers onto arbitrary substrates (e.g., SiO2/Si(001)) due to a weak van der Waals coupling at the MoS2 and Al2O3(0001) interface, facilitating vertical stacking strategies for monolithic integration of high quality and therefore high-performance, AlN-based piezoelectric devices and sensors on the Si platform.