Basic Research on Silicon Quantum Computation Based on Isotope Control and Neutron Irradiation

在硅基量子计算机中，^<31>P应作为量子比特分布在无自旋硅（自旋零^<28>Si或^<30>Si）中，距离约20 nm的阵列中。在本工作中，为了制备其基本器件结构，我们的目标是进行同位素控制硅层外延生长和中子辐照将^<30>Si转变为^<31>P的实验。这种在Si中分布^<31>P的方法优于离子注入技术，离子注入技术对深度具有固有的随机性。为此，首先，利用从俄罗斯Kurchatov实验室购买的富集的^<30>SiH_4，采用气源MBE法开发了几乎100% ^<30>Si的外延生长技术。因此，该无自旋硅外延层可用于硅基量子计算机的基底。利用该技术，我们成功地制备了天然Si/^<30>Si/天然Si （^<28>Si:^<29>Si:^<30>Si=92.2:4.7:3.1）同位素双异质结构，交替供应正常SiH_4和富集的^<30>SiH_4。然后，在日本原子能研究所用热中子通量1×10^<14> cm^<-2> s^<-1>辐照16h，将^<30>Si转化为^<31>P。通过精确的次级离子质谱（CAMECA-SIMS）测量，证实了^<30>Si形成^<31>P。其浓度约为5×10^<16> cm^<-3>w，与理论预测值基本一致。如果对^<29>Si/^<30>Si/^<29>Si双异质结构进行中子辐照，核自旋^<31>P将分布在无自旋硅（^<31>Si）中，将作为硅基量子计算机的基本结构。

In Si-based quantum computer, ^<31>P should be distributed in an array at a distance of about 20 nm in spin-free silicon (spin zero ^<28>Si or ^<30>Si) as a qubit. In the present work, in order to fabricate its basic device structure, we aim to perform the experiments on the epitaxial growth of isotopically controlled silicon layers and the transformation of ^<30>Si to ^<31>P by neutron irradiation. This method for distributing ^<31>P in Si is superior to the ion-implantation technique, which is inherently random to the depth. For this purpose, first, epitaxial growth technique of almost 100% ^<30>Si was developed by the gas source MBE method using enriched ^<30>SiH_4, which was purchased from Kurchatov laboratory, Russia. Thus this spin-free Si epitaxial layer can be available to the base for Si-based quantum computer. Using this technique, we succeeded to fabricate the natural Si/^<30>Si/natural Si (^<28>Si:^<29>Si:^<30>Si=92.2:4.7:3.1) isotope double hetero-structures by supplying alternately normal SiH_4 and enriched ^<30>SiH_4. Then, neutron irradiation was carried out to transform ^<30>Si to ^<31>P at Japan Atomic Energy Research Institute with thermal neutron flux of 1×10^<14> cm^<-2> s^<-1> for 16 h. By the precise secondary ion mass spectroscopy (CAMECA-SIMS) measurement, the formation of ^<31>P from ^<30>Si was confirmed. Its concentration was to be about 5×10^<16> cm^<-3>w, which was almost equal to the theoretically predicted value. If the neutron irradiation is performed to the ^<29>Si/^<30>Si/^<29>Si double hetero-structures, nuclear spin ^<31>P will be distributed in a spin-free silicon (^<31>Si ), which will be used as a basic structure of Si-based quantum computer.