DEFECTS IN PLASTICALLY DEFORMED SEMICONDUCTORS STUDIED BY POSITRON-ANNIHILATION - SILICON AND GERMANIUM

This paper is concerned with positron-annihilation studies in floating -zone silicon, which has been plastically deformed under high-stress a nd low-temperature conditions (HSLT). Positron lifetime spectra were d ecomposed into three components by means of the trapping model. Two de fect-related lifetimes were found to be constant (tau2 = 300 ps and ta u3 = 590 ps); they are constant during annealing. They are attributed to positron capture and annihilation by dislocation states (tau2) and microvoids (tau3). The microvoids (vacancy clusters) consist of at lea st ten vacancies. According to the model of diffusion-limited positron trapping, an upper limit of the microvoid concentrations is estimated . A pronounced increase of the microvoid-related trapping rate was obs erved after 600-degrees-C annealing of samples macroscopically deforme d in the HSLT step. The positron capture to dislocations is also descr ibed as diffusion limited and the dislocation densities obtained agree satisfactorily with densities measured by transmission electron micro scopy. Nonconservative dislocation motion and relaxation (jog dragging ) during annealing is proposed as an efficient vacancy-generation proc ess. Similar clustering effects were observed for HSLT-deformed high-p urity germanium at appropriately lower temperatures. The characteristi c defect-related positron lifetimes in Ge are determined to be tau2 = 325 ps and tau3 = 520 ps for dislocations and microvoids, respectively .