Silicon implanted with MeV(12)C ions; Temperature dependence of defect formation at low doses

Si(100) samples of n-type have been implanted with 3.6 MeV C-12 ions using doses < 10(7)-2 x 10(9) cm(-2). During implantation, the samples were kept at temperatures ranging from -110 to 400 degrees C, and subsequently, deep level transient spectroscopy (DLTS) was used for characterization of the samples. The DLTS spectra are dominated by the peaks normally associated with the vacancy-oxygen and divacancy (V-2) centers. The strength of the peaks changes with temperature and in particular, the level originating from the doubly negative charge state of V-2 increases by similar to 50% between -110 and 300 degrees C. This is not attributed to an increase in the V-2 concentration, but, merely reflects a relaxation of the strain in the lattice surrounding the V-2 centers. Above similar to 300 degrees C V-2 ceases to be stable and new energy levels appear. In particular, for doses below 10(7) cm(-2) at 400 degrees C a new major peak emerges close to the middle of the bandgap (similar to 0.57 eV below the conduction band edge, E(c)). The identity of E(c) -0.57 eV level is not known but it involves most likely impurities present in the as-grown material.