Abstract
It is proposed that the appearance of donor surface states at the silicon‐sapphire interface, after heating in moisture or hydrogen, is due to activation of impurities absorbed in the thin glassy layer which exists between the silicon and sapphire. This layer forms during deposition of the silicon films in a hydrogen atmosphere by reduction of the surface layer of sapphire, releasing aluminum into the silicon film. The photoconductivity of silicon‐on‐sapphire for photon energy below band gap energy is due to acceptor traps located more than 0.65 eV above the valence band.

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