Ion-beam-assisted nanocrystal formation in silicon implanted with high doses of Pb+ and Bi+ ions

In this paper we discuss ion-beam-assisted nanocrystal nucleation in amorph ized silicon (a-Si) layers produced by high-dose implantation of Pbl and Bi +. (100)-oriented Si wafers were implanted at room temperature (RT) with 50 keV Pb+ and Bi+ ions at doses ranging from 5 x 10(13) to 1 x 10(18) cm(-2) and a constant ion current density of 10 muA cm(-2). The resulting structur es were studied by conventional transmission electron microscopy (CTEM), hi gh resolution transmission electron microscopy (HRTEM) and Rutherford backs cattering spectroscopy (RBS) in combination with computer simulations. The dynamics of the ion-beam-induced crystallization of new phases and precipit ates evolution in the implanted layer were studied as a function of implant dose. It is established that the front of the new phase crystallization (c ubic Pb and hexagonal Bi nanocrystals) starts approximately at the peaks of the implanted species profiles; the crystallography of the nucleated nanoc rystal is examined as a function'of the dose.