AGGREGATION AND PRECIPITATION IN HIGH-DOSE AS ION-IMPLANTED GE0.5SI0.5 ALLOY

Thermally stimulated redistribution and precipitation of excess arseni c in Ge0.5Si0.5 alloy has been studied by X-ray photoelectron spectros copy (XPS), cross sectional transmission electron microscopy (XTEM) an d X-ray energy disperse spectrometry (EDS). Samples were prepared by t he implantation of 6 X 10(6) As+ cm(-2) and 100 keV with subsequent th ermal processing at 800 degrees C and 1000 degrees C for 1 h. The XPS depth profiles from the implanted samples before and after the thermal annealing indicate that there is marked redistribution of the element s in heavily arsenic-implanted Ge0.5Si0.5 alloys during the annealing, including: (1) diffusion of As from the implanted region to the surfa ce; (2) aggregation of Ge in the vicinity of the surface. A high densi ty of precipitates was observed near the surface which were by XTEM an d EDS identified as an arsenide. It is suggested that most of the impl anted As in Ge0.5Si0.5 alloy exists in the form of GeAs.