Anomalous electrical activation in Si-implanted GaAs/AlGaAs superlattices

Electrical activation in Si-implanted and annealed GaAs/AlGaAs superlattices (SLs) has been studied as a function of implantation temperature and dose. Carrier concentration, measured by the electrochemical capacitance-voltage profiling, is shown to be strongly dependent on implantation temperature. When SLs are implanted at room temperature or lower, electrical activation is severely suppressed in the near-surface region, where the carrier concentration is one to two orders of magnitude lower than the maximum (1-3)x1018/cm3 observed near the implant peak position. Similar deactivation behavior was observed in Si-implanted GaAs crystals, but the disparity between the minimum and maximum of the carrier concentration was significantly less than one order of magnitude. The minimum in carrier concentration profiles is explained in terms of carrier deactivation by the near-spherical voids of 25-200 A in diameter which are formed only in the near-surface regions, as revealed by transmission electron microscopy analysis. The larger carrier deactivation in the SL materials is attributed to the combined effects of electron confinement by the AlGaAs into the GaAs regions together with the preferential formation of voids in the GaAs layers. (orig.)