engleski

Vacancy related complexes in neutron irradiated silicon

It is evident from recent studies that there are profound differences in the defects produced by electron irradiation and ion implantation in silicon. The principal reason for this is the high damage rate near the end of range of the implanted particle which results in clusters of defects. Reverse modelling of annealing and ab initio calculations predict stable clusters of small numbers of vacancies and/or interstitials but it is extremely difficult to study these experimentally by techniques which give detailed electronic and structural information. Among the many reasons for this is that ion damage is extremely inhomogeneous resulting in a wide spatial distribution of different cluster sizes. To overcome this problem we have utilised fast neutrons to produce near uniform damage in silicon. In the work reported here we have used irradiation temperatures and flux densities which were expected to produce mostly small vacancy clusters in n- and p-type Cz silicon samples. These were studied by conventional and Laplace DLTS. The evolution of defects has been investigated using 30 min isochronal anneals. In n-type silicon three electron traps at 0.16 eV, 0.24 eV and 0.42 eV below the conducting band were observed. The E(0.16) and E(0.24) traps are VO and V2--/-, respectively. However an asymmetric peak at around 220K with an activation energy for electron emission of 0.42 eV dominates the spectra. We have used high resolution Laplace DLTS for investigations of the structure of E(0.42) and believe that this signal derives mainly from multivacancy clusters. From the annealing behaviour, it was found that as these clusters anneal out they are sources of vacancies for an increase in the concentration of VO and V2 as quantified from the LDLTS signals. Results on p-type support this analysis and are compared with previously published DLTS signals attributed to interstitial clusters in ion implanted material.

silicon; vacancy clusters; neutron irradiation; DLTS

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