Characterization of Electronic Charged States of Impurity Doped Si Quantum Dots Using Atomic Force Microsope/Kelvin Probe Technique

Abstract

Boron and phosphorous were doped into Si quantum dots (Si-QDs) by pulse injection of 1% B2H6 and PH3 diluted with He, respectively, during the self-assembling formation of Si-QDs from the thermal decomposition of pure SiH4 on a ∼4.2-nm-thick SiO2 layer thermally grown on a n+-Si(100) substrate. Electron charging and discharging of both the B- and P-doped Si-QDs were investigated to characterize their charged states by a Kelvin probe technique with a Rh-coated atomic force microscope (AFM) tip. Potential changes due to the extraction of one electron from the B- and P-doped Si-QDs were observed in applying the AFM tip biases of +2.0 and +0.2 V, respectively. At a tip bias of ∼1.0 V, potential changes observed in the case of undoped Si-QDs, whose size is almost the same as that of doped Si-QDs, were almost the same as those observed in the case of doped Si-QDs. Changes in the tip bias required for the electron extraction from Si-QDs by doping of B and P atoms are attributable to the difference in the electron emission process such that the emissions of a localized electron from an ionized B acceptor and a conduction electron caused by an ionized P donor need higher and lower tip biases than for the case of emission of a valence electron from undoped Si-QDs, respectively.