Oxygen - Impurity Interactions in Crystalline Silicon: the Cases of Aluminum and Erbium

Impurities such as oxygen and carbon have a strong influence on the electrical and optical behaviour of other species introduced in Si. The influence can be either beneficial or detrimental according to the considered case, Two different examples are discussed in the present paper. The electrical activity of ion implanted Al, the fastest diffusing p-type dopant, amounts to a few percent of the fluence in Czochralski wafers while is practically unity in epitaxial or float-zone wafers, having a low content of dissolved oxygen. This behaviour is accounted for in terms of Al-O inactive complexes whose formation is enhanced by defects, Good activation and deep junctions can be obtained by avoiding the simultaneous presence of O and defects. Erbium ions introduced by ion implantation in Si are optically active with an emission at 1.54 mu m. The luminescence, however, strongly quenches with temperature and room temperature emission cannot be achieved. The co-introduction of Er and O, with the subsequent formation of Er-O complexes in Si, strongly reduces this temperature quenching and room temperature light emission can be easily achieved, These two cases are presented and possible applications discussed.