학술논문
Effect of Sacrificial Mg2 Si Layers and Kinetic Parameters on the Growth, Structure, and Optical Properties of Thin Ca2 Si Films on Silicon Substrates
Document Type
Original Paper
Author
Source
Semiconductors. 56(7-12):367-381
Subject
Language
English
ISSN
1063-7826
1090-6479
1090-6479
Abstract
We simulate the conjugation of crystal lattices of two-dimensional Mg2 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 Ca2 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: Ca2 Si, CaSi, and hR3-CaSi2 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 Ca2 Si film is formed on Si(110) with the minimal contribution from CaSi. Polycrystalline and epitaxial Ca2 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 Ca2 Si(100)/Si(111) epitaxial ratio; as it increases from 7.3, polycrystalline films grow with three orientations on Si(111): Ca2 Si(100), Ca2 Si(110), and Ca2 Si(111). In Ca2 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 (E2d = 1.095 ± 0.1 eV).