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.
Microwave plasma using a gas mixture of N 2 and H 2 has been applied for the nitridation of m-plane sapphire substrate to form a thick epitaxial AlN film. The X-ray diffraction results show that the AlN films formed on the sapphire surface by nitridation for a period from 10-60 min are in (1010) orientation and have an epitaxial relationship with the substrate. The thickness of the nitride film increases with nitridation time and approaches about 0.5 μm after nitridation for 1 h, while the film surface becomes rough. The film quality is reasonably good, as evaluated with the X-ray rocking curve of (1010) AlN. Faceted voids in the sapphire substrate underneath the AlN are also observed with inclined a-plane facets after nitridation.
Charge transport studies have been performed on SiO films using an electron-beam injection technique· MOS capacitors incorporating oxides grown at 1000 and 1100°C were investigated, including units fabricated at Hughes Aircraft using radiation hardening p r o c e dures. A comparison of beam-induced current v s field characteristics is made for devices with differing pro cessing h i s t o r i e s . Additionally, experimental deter minations of trapped positive charge vs collected charge were performed. Present findings indicate that holes are mobile in SiO£, that the schubweg model is insufficient for describing charge transport in S1O2 films, and that the electron-hole pair creation energy for S i 0 2 i s ^ 19 eV. Current vs field data can be qualitatively explained in t e r m s of columnar and/or geminate recombination. Conclusions concerning the effects of processing on charge buildup are made and a qualitative model based on experimental findings is presented. Implications of this model for radiation hardening are discussed.
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