Energy levels of electrons trapped in buried oxide of SIMOX structures

The buried oxide (BOX) of SIMOX structures exhibits stronger electron trapping than thermally grown SiO/sub 2/ films and contains photo-active centers which can be positively charged. The electron traps with large cross section and the photo-active centers were ascribed to small Si clusters whose density is related to the oxygen implantation mode and subsequent processing. This work shows that the photo-active defects are of the same type in all the BOX layers but their size and density depend, among others, on the implantation energy, oxygen dose, and annealing conditions. If sufficient excess silicon is present in the BOX, then, in addition to amorphous Si clusters, crystalline Si islands form as well. The formation and stability of both types of Si inclusions are related to the confined nature of the BOX layer which, in turn, is affected by the Si substrate.