FUNDAMENTAL RESEARCH FOR QUANTUM DEVICES CONSTRUCTED WITH MULTI-LAYERS OF VERY THIN EPITAXIAL Al2O3 AND Si

在硅上异质外延生长绝缘层以及在这些绝缘层上连续生长单晶硅是形成绝缘体上硅(SOI)结构的一个重要方面。我们提出了γ-Al_2O_3薄膜作为绝缘材料，并在硅衬底上获得了高质量的γ-Al_2O_3薄膜。在本课题组中，我们已经研究了绝缘体上的硅结构，并提出了一种外延γ-Al_2O_3薄膜作为绝缘材料。采用Al固体源和N2O气体源的混合源分子束外延生长了γ-Al_2O_3薄膜。利用混合源MBE成功地在硅衬底上生长出了无碳污染的非常薄、非常平坦的γ-Al_2O_3薄膜。由于Al_2O_3绝缘层的稳定性，这种结构适合于常规的硅工艺。因此，γ-Al_2O_3有望成为一种可以替代SiO_2的绝缘膜。目前，本课题组正在研究γ-Al_2O_3在MIS型场发射体中的应用。此外，应用…由于由Si和γ-Al_2O_3形成的多层结构容易形成，量子效应器件有望获得更多的纳秒数。γ-Al_2O_3和Si的薄膜生长控制对于形成量子阱结构是非常必要的。因此，本研究的目的是对纳米厚度的生长进行控制，并利用Si和γ-Al_2O_3形成量子阱结构。由硅和绝缘膜组成的量子阱结构有望锁定高能电子，因为使用了对硅具有较大势垒高度的绝缘膜。因此，由Si和γ-Al_2O_3构成的量子阱结构在发射恒定电子能量的发射体中具有潜在的应用前景。计算结果表明，必须实现小于4 nm的硅膜厚度控制。随着γ-Al_2O_3的生长，在硅上直接生长的γ-Al_2O_3的电绝缘性能较差。而用Al_2O_3预涂层法制备的厚度为3 nm的γ-Al_2O_3薄膜可实现约5 mV/cm的电流密度。通过这种生长方法，实现了绝缘性良好的超薄薄膜(3 nm厚)的γ-Al_2O_3生长控制。到目前为止，硅的生长主要采用Si2H6气相生长，但薄膜厚度不可能控制在几nm以内。为此，提出了一种低增长速率的微束蒸发器装置。因此，这种方法可以实现低速生长(4 nm/小时)。但硅表面平整度的问题仍然存在。因此，我们提出了在γ-Al_2O_3表面进行Al封端的方法，即首先沉积Al，然后用800℃进行热处理。通过这种方法，在硅生长的早期阶段，我们成功地抑制了硅的三维生长。通过Al_2O_3预制层和Al的预沉积，形成了γ-Al_2O_3(3 Nm)/Si(111)(4 Nm)/γ-Al_2O_3(3 Nm)/Si(111)结构。然后，对其电学特性进行了评价。因此，在室温下确认为负阻。较少

Heteroepitaxial growth of insulating layers on Si and the successive growth of a single crystalline Si on those insulating layers are of great interest in the formation of silicon-on-insulator (SOI) structures. We have proposed γ-Al2O3 films as an insulator material and obtained high quality layers of γ-Al2O3 on Si substrates. In our group, we have already studied SOI(Silicon On Insulator) structures, and have proposed an epitaxial γ-Al2O3 film as insulator material. The epitaxial growth of γ-Al2O3 was investigated with the hybrid source MBE using Al solid source and N2O gas source. Very thin and very flat γ-Al2O3 films without carbon contamination were grown on Si substrates successfully by the hybrid source MBE.This structure is suitable for the usual Si process due to stable Al2O3 insulator. So γ-Al2O3 is being expected of an insulation film which can be substituted for SiO2. At present, our group are studying application to MIS type Field Emitter of γ-Al2O3. Furthermore, applicatio … More ns to quantum effect devices can be expected because multiple layer structure by Si and γ-Al2O3 can be formed easily. The very thin film growth control of γ-Al2O3 and Si becomes very necessary to form a quantum well structure. Therefore, the purpose of this study is the growth control of nm-thickness, and the formation of the quantum well structure by Si and γ-Al2O3. The quantum well structure composed of Si and an insulation film can be expected to lock up electrons of the high energy, because an insulation film with a large barrier height to Si was used. So the quantum well structure by Si and γ-Al2O3 has a potential application to an emitter which can emit a constant electron energy. As a result of the calculation, the thickness control of the Si film in less than 4nm must be realized. As growth of γ-Al2O3, an electrical insulation property of directly grown γ-Al2O3 on the Si was poor. But about 5MV/cm was realized using a 3nm-thick γ-Al2O3, which was prepared by Al2O3 pre-layer method. The γ-Al2O3 growth control of very thin film (3nm-thick) with good insulation property was realized by this growth method. Until now, Si2H6 gas sauce was used for the Si growth, but the control of film thickness of a few nm was impossible. So, the Mini-beam evaporator device with a low growth rate was introduced. So low speed growth (4nm/hour) became possible by this method. But a problem in Si surface flatness was still remained. So we proposed that termination of a γ-Al2O3 surface with Al, which is at first, deposition of Al, then annealing with 800℃. By this method, at the early stage of the Si growth, we succeeded in the repression of three-dimensional growth of Si. A γ-Al2O3 (3nm) /Si (lll) (4nm)/γ-Al2O3 (3nm)/Si (lll) structure was formed with Al2O3 pre-layer and Al pre-deposition. Then, the electrical characteristics were evaluated. As a result, a negative resistance was confirmed at room temperature. Less