Functional Cluster Method Research Articles

Structural properties of Na adsorbed on a Ge(100)2 × 1 surface: all electron, ab initio, density functional, cluster calculations

We present the first theoretical investigation of the structural properties of the Na Ge(100)2 × 1 system. The binding of a single Na atom at different possible adsorption sites on the Ge(100)2 × 1 surface was studied using DMol, an all electron, ab initio local density functional cluster method. In contrast to our previous results for the Na Si(100)2 × 1 system, we find the pedestal site to have the lowest total energy. This situation differs from the Si(100)2 × 1 surface where Na atoms were found to adsorb preferentially on the cave site. Furthermore Na atoms, when covalently bonded to the Ge dangling bonds tend to symmetrize the Ge dimer.

Ab initio investigation of the dislocation structure and activation energy for dislocation motion in silicon carbide.

The structures of straight 90\ifmmode^\circ\else\textdegree\fi{} glide partial dislocations in SiC are calculated using an ab initio local density functional cluster method. Si partials containing core Si atoms are found to be strongly reconstructed with a Si-Si bond of comparable length to that in bulk silicon. The C partial possessing core C atoms is more weakly reconstructed with a bond length 16% longer than that in bulk diamond. The formation and migration energies of kinks on the partials are calculated and indicate that the C partial is the more mobile. The calculations also predict that n-type doping leads to an increase in the mobility of C partials whereas p-type doping increases the mobility of Si partials.

Theory of Dislocations in GaAs

A local density functional cluster method is used to investigate the structure of dislocations in GaAs as well as their interaction with impurities. We find the 90° Ga(g) (β) partial is strongly reconstructed in the same way as in Si, but the As(g) (α) partial is not. This can account for the higher mobility observed for As(g) partials over Ga(g) ones. The influence of impurities on these core structures are discussed.

Density functional calculations of the structure and properties of impurities and dislocations in semiconductors

A local density functional cluster method is used to investigate the structure of dislocations in Si and GaAs as well as the interaction of P and O impurities with dislocations in Si. The 90° partial in Si is found to be strongly reconstructed but P impurities are strongly bound to the dislocation and inhibit this reconstruction. O impurities are also attracted to the core but form stable di-interstitial oxygen complexes there. These results can account for the strong pinning effects observed in plastically deformed Si containing these impurities. In GaAs, the 90° Ga(g) (β) partial is strongly reconstructed in the same way as in Si, but the As(g) (α) partial is not. This may account for the higher mobility observed for As(g) partials over Ga(g) ones.

First-Principles Calculations of Dislocations in Semiconductors

The structure of dislocations in semiconductors and the effect of their interaction with impurities are examined using an ab initio local density functional cluster method. This method is entirely free from any empirical parameters and takes account of the charge transfer between the impurity and the host as well as the forces acting on core atoms. It is found that dislocations in Si are strongly reconstructed but B, P, N, and As impurities destroy this reconstruction. C impurities have little effect. Oxygen atoms form clusters which aggregate near dislocation cores and also lead to strong pinning effects. These results explain the strong pinning effects attributed to these impurities. In GaAs, β-dislocations are strongly reconstructed but α-dislocations are not.