The composite substrate layer, a crucial buffer layer in Si-based HgCdTe materials, changes the epitaxial growth method of the ZnTe buffer layer within the composite substrate. The composite substrate is prepared by directly growing the ZnTe layer using a molecular beam epitaxy system. The substrate temperature is then adjusted to identify a process more suitable for direct epitaxy. Scanning electron microscopy (SEM), reflection high-energy electron diffractometer (RHEED), and white-light interferometry are used to investigate the effects of varying substrate temperature, buffer layer thickness, and epitaxial growth method on the material′s full width at half maximum (FWHM), phase deviation angle, roughness, RHEED patterns, and dislocation density. The results show that a thicker ZnTe buffer layer significantly reduces the dislocation density by an order of magnitude. By first growing a low-temperature seed layer and then epitaxially growing the ZnTe, the crystal orientation shift can be effectively reduced, resulting in even lower roughness.