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DISLOCATION NUCLEATION SILICON AND GERMANIUM

163 MODELS

FROM POINT DEFECT

CONDENSATIONS

IN

T.Y. Tan IBM T.J. Watson Research Center, Yorktown Heights, N.Y. 10598

ABSTRACT

The process of dislocation nucleation from point defect condensations in Si(Ge) is discussed. Based on the assumption that during the dislocation nucleation stage, the dominant factor in the configurational energy is the number of dangling bonds per point defect incorporated, rather than the more commonly recognized factor of strain energy, it is possible to model the dislocation nucleation process. In order to minimize the number of dangling bonds, point defects would condense into row configurations elongated in , called intermediate defects (IDC), and then the IDCs would evolute into undissociated 90' edge -, 600, and Frank partial dislocations.

INTRODUCTION

For many reasons the process of dislocation nucleation from condensations of point defects in Si(Ge) need to be studied. A most fundamental reason is that, being covalent materials, it is reasonable to expect the bonding nature of the atoms will influence the dislocation nucleation process to a significant extent so that it may be quite different from that in metals. There are a number of practical reasons too. To name a few important ones: (1). In electron, neutron and low dose ion damaged Si(Ge), simple point defects are usually produced. These are detectable by EPR, Raman or IR Spectroscopies because of their electrical activities.[11 After an annealing, however, such electrical activities cease and the defects are generally said to have been annealed out. Some such defects may have just disappeared due to vacancy-interstitial annihilation or migration to the surface, but it is very improbable that some of them did not aggregate together to form some sort of extended defect. Presently, it is not known just what such extended defects are but we could expect that some must be dislocations. (2). In high energy electron damaged thin Si(Ge) samples, and in thermally recrystallized, ion-implantation induced amorphous Si, there exists a peculiar class of defects not found in metals: the so-called rod-like defects (which, in our opinion, should also included {1131 stacking faults).[2-13] The mystery of this class of defects is so far unresolved. It is possible that they are dislocations in an early nucleating stage or defects with structures closely associated with the dislocation nucleation process. (3). In high dose rate implantation, the production rate of point defects is high and the probability of point defect coalasing into dislocations would also be high. Such coalasing processes need obviously to be studied. In this paper we present atomic models describing the manner by which point defects may condense and generate dislocations. The morphology, energetic and kinetic factors implied by the models are discussed.

164 MODELING

Assumptions. In crystalline materials, the free energy associated with a point defect is high, and in the presence of a large number of them in sup