Real-time evolution of trapped charge in a SiO2 layer: An electrostatic force microscopy study

Time-dependent motion of localized electrons and holes trapped in a SiO2 layer is visualized with electrostatic force microscopy. Both negative and positive charges of up to ∼1010 e/cm2 are trapped at a SiO2–Si interface in ∼500-nm-diam area with a voltage stress between the tip and the sample. There is a higher probability for trapped charges to spread out in the plane direction than to de-trap toward the Si substrate. The dynamics is explained with diffusion and drift of the charges induced by Coulombic interaction.