Decay characteristics of electronic charged states of Si quantum dots as evaluated by an AFM/Kelvin probe technique

Si quantum dots (Si-QDs) with an areal dot density of 8 x 10(11) cm(-2) on SiO2 have been prepared by the thermal decomposition of monosilane to characterize charged states of Si-QDs using AFM/Kelvin probe force microscopy (KFM). The temporal changes in the surface potential induced by electron charging and discharging at Si-QDs covered with a similar to 2-nm-thick oxide layer have been measured. In electron charging and discharging at Si-QDs, a Rb-coated AFM tip was electrically biased in the range of -5 to 5 V and scanned on the sample surface in a tapping mode. The surface potential changes on Si-QDs by electron injection and extraction were observable, while no potential change was detected elsewhere. The surface potential of charged Si-QDs decays with time at rates depending on charge injection conditions. The observed decay characteristics can be interpreted in terms of discharging of stored electrons in Si-QDs due to electron tunneling through the bottom oxide to the substrate and neutralization of stored holes due to recombination with electrons tunneling from the substrates. The defect generation in oxide is likely to be responsible for a fairly slow decay as observed in the case of electron extraction by the tip bias as high as +4.8 V with respect to p-Si(I 00). (c) 2005 Elsevier B.V. All rights reserved.