Scanning probe microscopy of single Au ion implants in Si

We have studied 5 MeV Au2+ ion implantation with fluences between 7 × 107 and 2 × 108 cm− 2 in Si by deep level transient spectroscopy (DLTS) and scanning capacitance microscopy (SCM). The DLTS measurements show formation of electrically active defects such as the two negative charge states of the divacancy (V2(/-) and V2(-/0)) and the vacancy-oxygen (VO) center. It is observed that the intensity of the V2(/-) peak is lower compared to that of V2(-/0) by a factor of 5. This has been attributed to a highly localized distribution of the defects along the ion tracks, which results in trapping of the carriers at V2(-/0) and incomplete occupancy of V2(/-). The SCM measurements obtained in a plan view show a random pattern of regions with a reduced SCM signal for the samples implanted with fluence above 2 × 108 cm− 2. The reduced SCM signal is attributed to extra charges associated with acceptor states, such as V2(-/0), formed along the ion tracks in the bulk Si. Indeed, the electron emission rate from the V2(-/0) state is in the range of 10 kHz at room temperature, which is well below the probing frequency of the SCM measurements, resulting in “freezing” of electrons at V2(-/0).