Roles of local He concentration and Si sample orientation on cavity growth in amorphous silicon

Abstract

International audience(111)- and (100)-oriented Si samples are implanted with Si⁺ ions at 1 MeV to a dose of 1×10¹⁶ cm^-2 and with 5×10¹⁶ He⁺ cm^-2 at 10keV or 50 keV and eventually annealed in the 800 °C-1000 °C temperature range. Sample characterization is carried out by cross section transmission electron microscopy, positron annihilation spectroscopy, and nuclear reaction analysis. In addition to the formation of He bubbles at the projected range of He, bubbles are observed after solid phase epitaxial growth (SPEG) of the embedded amorphous Si layer. The He threshold concentration required to get thermally stable bubbles in amorphized Si is between one and four orders of magnitude lower than in c-Si. Since bubble formation and growth take place in the a-Si phase, the interaction with SPEG during annealing is studied by considering (100) and (111) Si. Both the SPEG velocity and the resulting defects play a role on bubble spatial distribution and size, resulting in bigger bubbles in (111) Si with respect to (100) Si