Control of nano-scale quantum wire structures and optocal properties of one-dimensional excitons

(1)脊形量子线生长机理及形状控制的研究我们将超高真空原子力显微镜与分子束外延系统连接，实现了脊形量子线形成过程的原位观察。脊形量子线的形成过程如下。首先，（001）-（111）B面结构出现在梅萨形衬底上。在（001）-（111）B面的边界上还出现了（101）面和（112）面。当这些表面生长时，（001）表面消失。由于Ga原子掩埋了相邻的小平面，形成了非常光滑的脊结构。我们在衬底温度低于520 ℃的条件下成功地生长了10 nm尺度的脊形量子线。(2)纳米尺度量子线中一维激子的光学性质我们采用劈边过生长法制备了T型GaAs量子线，并测量了磁场下的空间分辨微光致发光。结果表明，在具有5 nm厚AlAs势垒的T型量子线中，横向约束能为38 meV，一维激子束缚能增加到27 meV。从光学各向异性的角度研究了价带的各向异性，与理论结果符合较好。从抗磁位移中，我们成功地观察到了波函数的空间范围对量子线宽度的依赖关系。从光致发光激发实验中还发现，当横向限制有效时，振子强度增加。

(1) Invesrigation of growth mechanism and shape control of the ridge quantum wireWe connected an ulfra high vacuum atomic force microscope to the molecular beam epitaxy system and realized an in-situ observation of the formation process of ridge quantum wire. Ridge quantum wire takes form throuhg the following process. First, (001)-(111) B facet structures appear on the mesa shaped substrate. On the border of (001)-(111) B facet, (101) surface and (112) surface also appear. As these surfaces grow, (001) surface disappears. Since Ga atoms bury vicinal facets, very smooth ridge strudture is formed. We made a successful growth of 10nm scale ridge quantum wire under the substrate temperature less than 520ﾟC.(2) Optical properties of one-dimensional exciton in the nm-scale quantum wireWe fabricated the T-shaped GaAs quantum wire by the cleaved-edge over-growth and measured spatially resolved micro photo luminescence in the magnetic fields. It was clarified that in the T-shaped quantum wire with 5nm-thick AlAs barriers the lateral confinementenergy was 38 meV and that the binding energy of one-dimentional exciton increased up to 27meV.We investigated the anisotropy of valence band from the optical anisotropy which was in good agreement with the theory. From the diamagnetic shifts, we successfully observed the dependence of the spatial extent of wave function on the width of quantum wire. It was also found that oscillator strength increased as lateral confinement was effective from the photo luminescence excitation experiment.