Void and Multivacancy Defects

Transition metal impurities have a large atomic radius and are readily attracted to voids or multivacancies. Indeed, there have been several studies of the gettering effect of voids [#!apl!#]. Within the void, there is a possibility of a molecular hydride species being formed as for example, AuH, AgH, PtH₂ and PdH₂. The molecular species are known to be thermally stable, e.g. AuH has a dissociation energy of 3.1 eV. To investigate their properties within Si, calculations were carried out on clusters containing a decavacancy whose surface is saturated with H. The ionisation energies and electron affinities of TMH hydrides inserted into this microvoid demonstrated that these defects possess no gap levels and as such represent a means by which the impurity is passivated. However, whereas it is known that voids form in plasma treated or H-implanted material, it is unclear whether they, or multivacancy centres, can be produced by wet etching.