Thin film diodes of Al-Aluminum Oxide-Metal structure were made by vacuum deposition and their electrical conduction mechanims were investigated. Alminum oxide films of several hundreds angstrom thickness were prepared by plasma oxidation. The oxide film is transparent from the wavelength of 3000Å to 20μ and the threshold value for fundamental absorption lies near 2370Å. From the fact the discharge current followed an inverse time law and the residual voltage build-up was proportional to log
t, it is concluded that trap levels are distributed in energy throughout the oxide films. The trap density is estimated to be more than 10
19 1/cm
3 and an electron capture cross section 7.4×10
-14cm
2. As the effect of traps was predominant in the oxide films, the current-voltage characteristics hold the relation for space-charge-limited current in the presence of traps, distributed in energy. The conclusion was confirmed by some numerical results.
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