Ion Beam Doping of MBE Silicon by As+

Abstract

ENERGETICSThe electrochemical data pertaining to Si and Si/PP electrodes in nonaqueous media can be explained by the presence of silicon surface states. In the case of n-Si/PP electrodes, it is suggested that oxidized PP is capable of extracting electronic charge from Si surface states, thus developing a positive charge on the n-Si surface (with respect to the bare surface). As the electrochemical potential of the polymer is made increasingly positive, the probability of electron extraction is greater. The slope of the V~ vs.Epp plot (Fig. 4) is less than unity indicating that the PP film causes a change in both the surface state charge and the degree of band bending.A similar interpretation is given for p-Si/PP electrodes. In this case, two mechanisms leading to bandedge unpinning are evident: (i) when the occupied energy levels of the PP film lie above those of p-Si surface states, electron injection from PP to the surface states occurs, resulting in the raising of the flatband potential to more negative potentials; and (ii) when Epp is below the energy associated with surfacestates, electron extraction from the latter occurs, decreasing the negative charge at the Si/PP interface. The energy barrier between Epp and the Si valence band energy decreases as Epp is made more positive, and the p-Si/PP interface correspondingly changes from rectifying to ohmic. Quasi-ohmic behavior of p-Si/PP electrodes in nonaqueous media has been previously reported (9). C-V experiments show that the flatband potential of p-Si shifts by 500 mV for a 600 mV change in Epp, indicating that substantial Fermi level pinning is present. Measurement of the open-circuit photovoltage as a function of Epp were consistent with values predicted by the relation VpH = IVrB -EPPI. ConclusionBandedge unpinning of n-and p-type Si in CH3CN is clearly evident in the presence of a PP film, a redox couple, or both. The phenomenon is a result of facile electron transfer between PP and surface states located within OF ELECTRON TRANSFER 3109 the Si bandgap region. PP undergoes rapid equilibration with the ferrocene redox couple in solution and thus facilitates electron transfer between the Si electrode and the solution species. This insight into the energetics of electron transfer between PP coated semiconductors and redox species in solution is important in the design of conducting polymerbased PEC cells. ABSTRACTThe incorporation and electrical activation of As + ions simultaneously implanted in Si(100) epilayers during MBE growth (700~ are reported. Bulk-like mobilities, 100% activation, and excellent crystalline quality were obtained using 1 keV As + ions at growth rates 0.1-0.3 nms -1. No deterioration in crystal quality was found as the As level was varied from 10 TM to 2 9 1020 cm -3 at 700~ but at lower growth temperatures, As solubility limited the incorporation of As on substitu-) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.182.74 Downloaded on 2015-06-04 to ...