Hole and electron transport in SiO2 films

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Abstract
Carrier transport in SiO2 has been studied by exciting hole‐electron pairs in an oxide film by a pulsed electron beam. The energy of the beam (4–8 kV) was chosen to minimize excitation in the Si substrate upon which the SiO2 was grown. Measurements of oxide current vs applied voltage were made with beam intensity and energy as parameters for SiO2 layers of three thicknesses. It is demonstrated that normalized current‐vs‐field curves are independent of beam intensity, beam energy, and film thickness over the range studied. These results indicate that the analysis used by various workers to determine the mobility‐lifetime (μτ) product for SiO2 is invalid. Observed dependences of current on applied field can best be explained by geminate and/or columnar recombination. The present findings indicate that both holes and electrons traverse most of the SiO2 without appreciable permanent trapping. The amount of positive charge trapped at or near the SiO2–Si interface is a significant fraction of the ``collected'' charge, indicating that some of the holes that move to the interface do not penetrate it.