Defects in plastically deformed semiconductors studied by positron annihilation: Silicon and germanium

Abstract

This paper is concerned with positron-annihilation studies in floating-zone silicon, which has been plastically deformed under high-stress and low-temperature conditions (HSLT). Positron lifetime spectra were decomposed into three components by means of the trapping model. Two defect-related lifetimes were found to be constant (${\mathrm{\ensuremath{\tau}}}_{2}$=300 ps and ${\mathrm{\ensuremath{\tau}}}_{3}$=590 ps); they are constant during annealing. They are attributed to positron capture and annihilation by dislocation states (${\mathrm{\ensuremath{\tau}}}_{2}$) and microvoids (${\mathrm{\ensuremath{\tau}}}_{3}$). The microvoids (vacancy clusters) consist of at least 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 observed after 600 \ifmmode^\circ\else\textdegree\fi{}C annealing of samples macroscopically deformed in the HSLT step. The positron capture to dislocations is also described as diffusion limited and the dislocation densities obtained agree satisfactorily with densities measured by transmission electron microscopy. Nonconservative dislocation motion and relaxation (jog dragging) during annealing is proposed as an efficient vacancy-generation process. Similar clustering effects were observed for HSLT-deformed high-purity germanium at appropriately lower temperatures. The characteristic defect-related positron lifetimes in Ge are determined to be ${\mathrm{\ensuremath{\tau}}}_{2}$=325 ps and ${\mathrm{\ensuremath{\tau}}}_{3}$=520 ps for dislocations and microvoids, respectively.