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Interplay between structural changes, surface states and quantum confinement effects in semiconducting Mg 2 Si and Ca 2 Si thin films.
- Source :
-
Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2023 Jul 26; Vol. 25 (29), pp. 19952-19962. Date of Electronic Publication: 2023 Jul 26. - Publication Year :
- 2023
-
Abstract
- Ab initio techniques have been used to investigate structural changes in semiconducting Mg <subscript>2</subscript> Si and Ca <subscript>2</subscript> Si thin films (from 17 nm down to 0.2 nm corresponding to the 2D structure) along with band-gap variations due to quantum confinement. Cubic Mg <subscript>2</subscript> Si(111) thin films being dynamically stable at thicknesses ( d ) larger than 0.3 nm displayed an indirect band gap, the reduction of which with increasing d could be reasonably well described by the simple effective mass approximation. Only 2D Mg <subscript>2</subscript> Si has a unique structure because of the orthorhombic distortion and the direct band gap. Since the surface energy of cubic Ca <subscript>2</subscript> Si(111) films was lower with respect to any surface of the orthorhombic phase, which is the ground state for the Ca <subscript>2</subscript> Si bulk, the metastable in-bulk cubic phase in the form of thin films turned out to be preferable in total energy than any orthorhombic Ca <subscript>2</subscript> Si thin film for d < 3 nm. Sizable structural distortion and the appearance of surface states in the gap region of Ca <subscript>2</subscript> Si thin films with d < 3 nm could be the reason for an odd dependence of the band-gap variation on d .
Details
- Language :
- English
- ISSN :
- 1463-9084
- Volume :
- 25
- Issue :
- 29
- Database :
- MEDLINE
- Journal :
- Physical chemistry chemical physics : PCCP
- Publication Type :
- Academic Journal
- Accession number :
- 37458752
- Full Text :
- https://doi.org/10.1039/d3cp01878d