Study on Nanofabrication and Electron Wave Devices

今年取得的成绩，可以分为以下三个方面。我们用低能聚焦离子束(FIB)在Au或GaAs衬底上直接沉积形成了硅岛。采用低能FIB选区掺杂和分子束外延再生长的方法制备了埋入的二维电子层，用C-V法测量了不同退火条件下的载流子分布。该技术适用于电子波器件的制作，但生长中断在全真空工艺中存在许多问题。因此，我们从实验和理论上对生长中断效应进行了研究。研究发现，由生长中断引起的载流子耗尽量与Si掺杂浓度有关。通过对薛定谔方程和泊松方程的自洽计算，得出这种依赖关系是由浅界面态引起的。因此，生长中断在制造过程中甚至在…中造成严重影响在超高真空室里有更多。为此，我们研究了As的钝化效应，发现As的钝化有效地降低了界面态密度。现场处理仪为了降低生长中断引起的界面态密度，在低能FIB腔体中增加了一个离子泵，改进了电子延缓电路，实现了微细聚焦，实现了亚微米级的聚焦。我们研究了非对称偏置对金属分裂门量子点接触中限制势的影响。我们利用电子束光刻技术(剑桥大学)、Ar离子刻蚀技术(大阪大学)和反应离子刻蚀技术(剑桥大学)成功地制备出直径为40 nm、间距为100 nm的反点超晶格。应用该工艺技术实现了铬和三氧化二铬的小隧道势垒。

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