Effect of Sacrificial Mg2Si Layers and Kinetic Parameters on the Growth, Structure, and Optical Properties of Thin Ca2Si Films on Silicon Substrates

We simulate the conjugation of crystal lattices of two-dimensional Mg 2 Si layers with atomically clean Si(001)2×1 and Si(110)"16×2" surfaces. Thick films are grown by molecular-beam epitaxy (MBE) through the formation of Ca 2 Si seed layers. For a Si(001) substrate, three different silicides are formed in a 140-nm thick film at a temperature of T = 300°C at a Ca-to-Si deposition rate ratio of 4.7: Ca 2 Si, CaSi, and hR3-CaSi 2 with comparable contributions. With a decrease in the MBE-growth temperature to 250°C and a Ca-to-Si deposition-rate ratio of 8.4, a polycrystalline Ca 2 Si film is formed on Si(110) with the minimal contribution from CaSi. Polycrystalline and epitaxial Ca 2 Si films with thicknesses from 22 to 114 nm are grown on Si(111) substrates by the sacrificial-template method and MBE growth at a temperature of 250°C and different ratios of Ca and Si deposition rates (4.0–20.0). The minimum deposition-rate ratio ensures single-phase growth with the Ca 2 Si(100)/Si(111) epitaxial ratio; as it increases from 7.3, polycrystalline films grow with three orientations on Si(111): Ca 2 Si(100), Ca 2 Si(110), and Ca 2 Si(111). In Ca 2 Si films, regardless of their structure, the fundamental transition is masked by the Urbach edge in the photon-energy range of 0.78–1.0 eV, and then the second direct interband transition is identified ( E 2 d = 1.095 ± 0.1 eV).