Study on Nanofabrication and Electron Wave Devices

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The achievements of this year can be divided into the following three subjects.1. In-situ processWe succeded to form Si island by direct deposition on Au or GaAs substrate using low-energy focused ion beam (FIB). Buried two-demensional electron layrs were fabricated using selective-area doping by low-energy FIB and regrowth by MBE.The carrier profile was measured using C-V method with various anneal conditions. This technique is applicable to fabrication of electron-wave devices.Growth interruption causes many problems in the total-vacuum processing. Therefore, we investigated the effect growth interruption experimentally and theoretically. It was found that the amount of carrier depletion caused by growth interruption depended on the Si doping concentration. It was concluded by the self-consistent calculation of Schrodinger and Poisson equations that the dependence was due to the shallow interface states. The growth interruption thus causes sever effect in the fabrication process even … More in the ultra-high-vacuum chamber. Therefor we investigated the passivation effect using As and found that As passivation is effective to reduce the interface-state density.2. In-situ processing instrumentIn order to reduce the interface-state density caused by the growth interruption, an additional ion pump was added to the chamber for low-energy FIB.We improved the electronic circuit for retarding to achieve fine focus, and it was confirmed that the sub-micron diameter was realized.3. Electron-wave deviceWe investigated that the effects of asymmetric bias on the confinement potential in the quantum point contact of metal split gates. We successfully fabricated that an anti-dot superlattice using electron beam lithography (University of Cambridge), Ar ion etching (Osaka University) and reactive ion etching (University of Cambridge), which has the dots of 40-nm diameter and 100-nm pitch.We developed the selective-area oxidation process using electron beam. We applied the process technique to realize small tunneling barrier of Cr and Cr_2O_3. Less