| Research Abstract |
This project aimed at constructing high-functional integrated circuits composed of electron devices, optical devices, and opto-electronic devices utilizing metal/insulator/semiconductor superlattices on silicon substrates. In order to realize such integrated circuits, we achieved well controlled epitaxial growth of CaF_2/CdF_2 and Si/CaF_2 superlattices which are suitable for high-functional devices due to their very high band offsets resulting in remarkable quantum effects. We then fabricated resonant tunneling devices with these superlattices, and ultra-short channel Schottky source/drain MOSFETs to be integrated with the resonant tunneling devices.
For the epitaxial growth and its application to resonant tunneling devices, we established the growth condition by using ionized beam epitaxial technique, and obtained resonant tunneling diodes with the peak-to-valley ratio of the negative differential resistance as high as 10^5. The crystalline quality of the epitaxial layers were further
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improved by a selective growth into windows with a few hundred nanometer size made on silicon substrate by SiO_2 masks. By this method resonant tunneling diodes with high uniformity, reproducibility, and large peak-to-valley ratio were obtained at room temperature.
Ultra-short channel MOSFETs with Schottky sources and drains were fabricated with PtSi for p-type and ErSi_2 for n-type devices. Room-temperature operation of the devices with the channel length as short as 25nm was achieved. On/off ratio was shown to be increased by the use of SOI substrates with the thin silicon layers. As a transistor structure suitable for integration with the resonant tunneling diodes, vertical Schottky source/drain p-MOSFETs were fabricated, and transistor action was achieved at room temperature for the devices with channel width 8nm and channel length 50nm. By these results, we believe that fabrication process and fundamental operation of the basic elements for high-functional quantum-effect devices and their integrated circuits on silicon substrates were established. Less
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