Ja. Cogordan et al., AMORPHOUS CLUSTERS .3. THE ELECTRONIC-STRUCTURE OF SI CLUSTERS WITH BAND AL IMPURITIES, Journal of non-crystalline solids, 181(1-2), 1995, pp. 135-145
Amorphous clusters of the type XSi(20)H(28) with X=B and Al have been
studied using the pseudopotential SCF Hartree-Fock and the HONDO progr
am. The local electronic density of states and the charge density were
obtained for structures determined by energy optimization of the posi
tion of the central impurity, and of the position of the central impur
ity and the four nearest neighbors, using the AM1 method implemented i
n the MOPAC program. The structures obtained in this manner are such t
hat the impurities are not located at the center of the dusters; inste
ad both the boron and the aluminum are displaced towards three of the
four nearest neighbors, a fact that indicates that there is a tendency
for the impurity to remain with the same chemical valence in the clus
ter as when isolated. The gap energy states introduced by both B and A
l are near the valence band and are p-like; the state due to aluminum
is closer to the valence band than the one introduced by boron. These
results are compared with recent experimental findings.