Periodic Modulation of Superlattice by Atomic Layer Epitaxy and Its Application to synthesis of Novel Functional Materials

通常的周期结构中的电子态是由像布洛赫定理那样的周期性给出的。在晶格中引入非周期性，可以期望电子波函数具有奇异相干性的电子态。我们重点研究了晶格的周期调制（分形等），并进行了周期调制超晶格作为新型功能材料的制备和表征。本研究结果总结如下：(1)超晶格原子层操纵技术的发展：通过原子层外延（ALE）成功实现了（GaAs）m(GaP)n和（AIP）m(GaP)n原子层超晶格，并讨论了单层晶格之间的相互扩散。(2)具有原子层精度的超晶格周期性调制：利用ALE技术成功地实现了GaAs/GaP和AlP/GaP具有原子层精度的周期性调制超晶格。周期结构、拟周期结构（分形）、随机结构、多周期结构被用作调制结构，特别是斐波那契级数被用作分形结构。(3)周期调制超晶格的x射线分析：准周期超晶格的XRD谱图不具有周期性，但具有自相似的几何形状，与分形结构的FFT谱相一致。对多周期超晶格的x射线反射测量表明，可以通过调制周期来控制反射波长，达到亚单层精度。这表明了应用于x射线反射镜的可能性。(4)周期调制超晶格中电子态的光学表征：与周期晶格相比，准周期、随机超晶格的光反射光谱显示出子带（电子态）的特殊分裂，并且与晶格的传递矩阵计算相一致。这一结果表明，利用ALE技术进行周期调制可以人为地控制电子状态。(5)在x射线反射镜中的应用：讨论了晶格周期调制在x射线反射镜中的应用。在原子层超晶格中引入多周期，可以任意控制反射波长，达到x射线反射镜所需的亚单层精度。少

Electronic states in usual periodic structures are given by the periodicity like Bloch theorem. Introducing non-periodicity into the lattice, the electronic states with singular coherency of electron wavefunctions can be expected. We have focused on the periodic modulation (Fractal etc.) of lattice, and carried on the fablication and the characterization of periodic-modulated superlattices, as novel functional materials. The results of this study are summarized as follows.(1)Development of atomic-layer manipulation technologies for superlattice : (GaAs)m(GaP)n and (AIP)m(GaP)n atomic-layer superlattices have been successfully realized by atomic layer epitaxy(ALE), and also the inter-diffusion between the mono-layer lattice has been discussed.(2)Periodic modulation of superlattice with atomic-layer accuracy : GaAs/GaP and AlP/GaP periodic-modulated superlattices have been successfully realized with atomic-layer accuracy by the ALE technologies. Periodic, quasi-periodic (Fractal), random … More , and multi-periodic structures have been used as the modulated structures, and especially Fibonacci progression has been used as Fractal structures.(3)X-ray analysis of the periodic-modulated superlattices : The XRD pattern of quasi-periodic superlattice shows no periodicity but self-similar geometry, and is consistent with the FFT spectrum of a Fractal structure. Also the X-ray reflection measurement of multi-periodic superlattice shows that the reflection wavelength can be controlled with sub-monolayer accuracy by modulation of the periodicity. This suggests the possibility of application to X-ray mirrors.(4)Optical characterization of electronic states in the periodic-modulated superlattices : Photo-reflectance spectrum of quasi-periodic, random superlattices show peculiar splitting of the subband (electronic states) in comparison with that of the periodic lattice, and are consistent with a transfer matrix calculation for the lattices. This result suggests that the control of electronic state can be possible artificially due to the periodic modulation using the ALE technologies.(5)Application to X-ray mirrors : We have discussed the application of periodic modulation for the lattice to X-ray mirror. Introducing the multiple period into atomic layer superlattice, the reflection wavelength can be controlled arbitrary with sub-monolayer accuracy that is needed to X-ray mirrors. Less