Silicon implanted with MeV 12C ions; temperature dependence of defect formation at low doses

Abstract

Si(100) samples of n-type have been implanted with 3.6 MeV 12C ions using doses < 10 7−2 × 10 9 cm −2. During implantation, the samples were kept at temperatures ranging from −110 to 400°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 ∼ 50% between −110 and 300°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 ∼ 300°C V 2 ceases to be stable and new energy levels appear. In particular, for doses below 10 7 cm −2 at 400°C a new major peak emerges close to the middle of the bandgap (∼ 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.