IRON ALUMINUM PAIRS IN SILICON

Iron-aluminum pairs in silicon are investigated with conventional and optically detected electron paramagnetic resonance (EPR). For the trigonal and orthorhombic pairs known from previous EPR measurements we found for the first time optical absorption bands by measuring their magnetic circular dichroism of the absorption (MCDA). Direct experimental evidence is presented for the configuration bistability of both pairs by showing that the MCDA of the trigonal configuration can be transformed into that of the orthorhombic configuration by the combined effect of light and temperature. A new trigonal pair was discovered by conventional EPR having the same EPR intensity as the known one. Total energy calculations of various (Fe(i)-Al(s)) pair configurations show that two trigonal (Fe(i)-Al(s))o pairs with different Fe(i)-Al(s) separations have almost the same binding energy and should occur with the same probability. Fe(i)+ is always on a tetrahedral interstitial site, while Al(s)- is nearest neighbor along <111> in one pair, second nearest neighbor in the other one with one silicon lattice site in between.