ON THE SENSITIVITY OF POSITRONS TO ELECTRIC-FIELDS AND DEFECTS IN MBE-GROWN SILICON STRUCTURES

The sensitivity of the positron to the internal electric fields in goo d quality thin (almost-equal-to 100 nm) Molecular Beam Epitaxy (MBE)-g rown layers is experimentally demonstrated. Both a thin intrinsic laye r grown on a p-type substrate and a highly n-doped delta profile burie d in intrinsic silicon form effective barriers to positron diffusion a lthough no defects can be detected. We also extract, from a full treat ment of the positron diffusion, a quantitative estimate of the concent ration, below the detection limits of other methods, of large vacancy clusters in a thick (680 nm) film.