Free charge carriers in mesoporous silicon

Free charge carriers in mesoporous Si (meso-PS) consisting of Si nanocrystals of small dimensions of about 6-10 nm are investigated by the infrared-absorption technique, Adsorption of acceptor molecules or filling the pores with dielectric liquids are found to increase the concentration of free holes (p) in meso-PS up to the half of the doping level of the heavily boron-doped p(+)-Si substrate (p similar to5 x 10(18) cm(-3)) from which the meso-PS was made. Considering the value of p and the dc electrical conductivity sigma, the hole mobility is determined as about 5 x 10(-4) and 5 x 10(-3) cm(2) V-1 s(-1) for as-prepared meso-PS and meso-PS filled with a polar dielectric liquid, respectively. The activation energy is larger for sigma, than for p giving evidence for thermal activation of the hole mobility. A model of the dielectric confinement for charge carriers and hydrogenic impurities is applied to explain the dependence of sigma and p on the dielectric constant of the ambience of the Si nanocrystals.