Thermal evolution of defects in H-implanted Si studied by monoenergetic positrons

The behavior of hydrogen-vacancy defects in silicon implanted with H ions ( 1x10(16)/cm(2), 60 keV) has been investigated by means of a slow positron b eam, in which both the positron lifetime and the Doppler broadening have be en measured. It has been found that the positron-trapping defect associated with H is formed within the H implantation profile. This gives rise to a l ong positron lifetime, which is close to that characteristic of a monovacan cy. However, the Doppler broadening parameter S of this defect is not as la rge as that of the monovacancy, since positrons annihilate electrons of H w ithin the defect. Upon annealing at up to 400 degrees C, the defects locate d within 350 nm of the surface are agglomerated and also hydrogenated, wher eas the H-decorated defects within the H implantation profile are unchanged . Hydrogenation stabilizes and immobilizes the defects in this temperature range. Annealing at 500 degrees C leads to the agglomeration of the H-decor ated defects in the vicinity of the peak of the hydrogen implantation profi le. Annealing at 600 degrees C leads to hydrogen release from these agglome rates. It has been found that a high density of hydrogen-stabilized defects is present within the implantation profile upon annealing at 400 degrees C . This high density allows for the formation of larger vacancy clusters upo n higher temperature annealing. [S0163-1829(98)00443-3].