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Ab initio studies of early stages of nitride growth process on silicon carbide
|Elwira Wachowicz 1, Malgorzata Sznajder 2, Jacek A. Majewski 3|
1. Wrocław University, Institute of Experimental Physics (IFDUWr), plac M.Borna 9, Wrocław 50-204, Poland
|Thin nitride films are still attracting much interest because of their potential applications in opto- and microelectronics. An important substrate for epitaxial growth of AlN and GaN layers is SiC, since it is nearly lattice matched with AlN and has relatively low misfit with GaN. Nitride heterostructures are mainly grown on the 4H- and 6H-SiC with the growth direction along the hexagonal c-axis. Such heterovalent heterostructures exhibit the built-in macroscopic electric fields  that originate from (i) the heterovalent character of the interface, and (ii) piezo- and pyroelectric character of the constituent bulk materials. In spite of considerable experimental [1,2] and theoretical efforts [3-5], the physical understanding of these intriguing interfaces is still incomplete.|
In this paper, we present results of ab initio density functional theory calculations of formation of Al, Ga, and N layers on 4H and 6H silicon carbide surfaces. These studies provide us physical insight in the first stages of the formation of AlN and GaN layers on hexagonal SiC. We use slab geometry consisting of 12 layers with the ‘bulk’ end of the slab saturated with hydrogen atoms and employ SIESTA package. We consider ideal as well as reconstructed surfaces of SiC with Al, Ga, N coverages of 0.25, 0.33, 0.5, and 1 mono layer (ML) with adatoms placed originally into all possible localizations at the surface. The full relaxation of the geometry is performed for the upper layers (the lowest one are kept rigid to simulate bulk region) and the energetically favorable positions of the adatoms are determined. Further, the formation enthalpies, charge distribution around the adatoms, and macroscopically averaged charge and potentials are computed. For some cases, we have also calculated the potential path of the adatom for the move from the one adsorption position to the other. Interestingly, we find out that for the Ga layer on the Si terminated 4H-SiC surface, the adsorption energy diminishes with the growing coverage (from -5.39 to -8.95 ev/atom), however, Al layer generally does not follow this trend. Our study indicate that ideal single Ga (or Al) layer can be stable on top of Si one, whereas some kind of the intermixing must occur to stabilize such interface in the bulk material .
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Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 9, by Jacek A. Majewski
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-07-17 01:46 Revised: 2013-07-18 13:27