Study on epitaxial metal/insulator multilayr structure formation

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Ionized cluster beam (ICB) method has been used to form thin films of metals, insulators and so on which have unique characteritics when compared to films formed using other techniques. The ICB method has also been applied to low temperature growth of epitaxial films on substrates having a large lattice mismatch.Al/Al_2O_3 multilayr structures are suitable candidates for high speed quantum effect devices, because of the large band offset at the interface, high carrier density of the metal and high breakdown field in the insulator. We have grown epitaxial Al/Al_2O_3 multilayr structure on Si(111) substrates by ICB method. The surface state and crystallinity were studied by STM,TEM and RHEED.It was found that the epitaxial growth of Al on Al_2O_3 and of Al_2O_3 on Al was achieved, and that the interface between Al and Al_2O_3 layrs was flat. In addition, we have succeeded to fabricate triple barrier resonant tunneling diodes using epitaxial Al/Al_2O_3 multilayr structures on Si(111) substrates and observed negative differential resistance. The resonant voltage was 1.22 V and the peak-valley ratio was 1.003. The value of resonant voltage agreed with the calculated value using Trasfer Matrix Method. The epitaxial Al/Al_2O_3 multilayr structure can be expected to be applied to quantum effect devices.