Co-growth of 3D Si and 2D Si2Te3 Crystals: Roles of Catalysts and Effects of Catalyst Stabilities

Growth mechanism study is important to achieve high-quality materials growth using more convenient approaches and to realize controlled growth with compositional and structural tunability. In vapor-based deposition, vapor-solid (VS) and vapor-liquid-solid (VLS) processes have been two classic mechanisms for the growth of micro- and nano-scale structures. The VS process is a non-catalyst growth controlled by vapor supersaturation, while the VLS process is a catalyst-assisted growth initiated and guided by eutectic particles. This research reported a co-growth of three-dimensional (3D) Si crystals with two-dimensional (2D) Si2Te3 crystals and explored its growth mechanism. Chemical vapor deposition (CVD) method has been employed using Te and Si powders as the source materials in the presence of a Cu-coated Si substrate. The growth mechanism study reveals that the Te source plays two different roles in the growth. First, it serves as a reactant which vaporizes and reacts with Si powders to yield 2D Si2Te3 growth via the VS mechanism. A unique “liquid epitaxial growth” was discovered that Te droplets formed prior to the Si2Te3 growth could promote a quasi-epitaxial growth of Si2Te3 crystals on a lattice mismatch substrate. Second, the Te serves as an unstable catalyst for the 3D Si growth. The Si growth is promoted by the synergistic effects of Cu and Te: (1) Cu as a stable catalyst facilitates the reaction of Te vapor species with the Si substrate, forming ternary Te-Cu-Si eutectics; (2) due to the instability of Te, the Te-Cu-Si eutectic particles evaporate and release Si vapor as the precursor for the VS growth of Si crystals. This intermediate process is dubbed as a vapor-liquid-vapor (VLV) process which provides a new approach for the material growth with lower growth temperature, lower cost, and higher compatibility for device fabrications.