Growth Dynamics and Properties of Compound Semiconductor Layers Prepared by Low Temperature Molecular Beam Epitaxy

采用低温（LT-）分子束外延法（MBE）生长III-V型半导体和/或稀释磁性半导体及其纳米结构。利用反射高能电子衍射（RHEED）、原子力显微镜（AFM）和磁力显微镜（MFM）对其生长动力学和结构进行了研究。对样品的光学、磁性和输运性质也进行了表征。研究结果总结如下：1。当生长温度大大降低（~ 300℃）时，RHEED强度的振荡恢复。基于将过量砷视为自表面活性剂的模型，用蒙特卡罗模拟计算成功地表示了温度依赖性的实验结果。用MBE法制备了一种Mn浓度仅为百分之几的新型稀释磁性半导体（Ga,Mn）Sb。通过原子力显微镜（AFM/MFM）、磁化和磁输运测量研究了它们的性质与生长温度的关系。通过原子力显微镜（AFM）和原子力显微镜（MFM）观察，发现在表面形成了MnSb团簇。当生长温度高达~ 560℃时，样品在室温下呈铁磁性，微晶硅簇主导了整个磁化性能。另一方面，在低温下生长的样品的磁化和磁输运性质在20 K以下表现出另一种磁相，表明（Ga,Mn）As在较低温度（~ 20 K）下变为铁磁性。结果表明，在（211）B GaAs衬底上生长的自组装InMnAs量子点的尺寸均匀性可以通过引入Mn而得到改善，表明Mn起到了表面活性剂的作用。采用LT-MBE制备了全半导体铁磁体（GaMn）As/非磁体（Al,Ga）As/铁磁体（Ga,Mn）As三层结构，并对其磁性和输运性质进行了表征。研究表明，两个铁磁层之间的磁耦合可以通过调节非磁性层的厚度和/或势垒高度来控制。此外，我们还首次在该体系中观察到巨磁阻效应。少

III-V semiconductors and/or diluted magnetic semiconductors, and their nanostructures were grown by low-temperature (LT-) molecular beam epitaxy (MBE). The growth dynamics and structures have been investigated by reflection high energy electron diffraction (RHEED), and atomic force (AFM) and/or magnetic force (MFM) microscopy. Their optical, magnetic, and transport properties of the samples were also characterized.The summary of the research results are :1. It has been observed that the oscillation of the RHEED intensity recovers as the growth temperature was much lowered (〜300℃). The experimental results of the temperature dependence were successfully represented by Monte-Carlo simulation calculation based on the model which treats the excess arsenic as self-surfactant.2. A new diluted magnetic semiconductor (Ga,Mn)Sb with a few percent Mn concentration has been successfully grown by MBE. The dependence of their properties on the growth temperature was investigated by AFM/MFM, magneti … More zation and magnetotransport measurements. By AFM and MFM observations, it was found that MnSb clusters were formed on the surface. When the growth temperature is as high as 〜560℃, the sample is ferromagnetic at room temperature, and the MnSb clusters dominate the whole magnetization properties. On the other hand, the magnetization and magnetotransport properties of the samples grown at LT exhibit another magnetic phase below 20 K, indicating the existence of (Ga,Mn)As which becomes ferromagnetic at lower temperatures (〜20 K).3. It has been demonstrated that size uniformity of the self-assembled InMnAs quantum dots grown on (211)B GaAs substrate can be improved by introducing Mn, indicating that Mn plays a role of surfactant.4. All-semiconductor ferromagnet (GaMn)As/nonmagnet (Al,Ga)As/ferromagnet (Ga,Mn)As trilayer structures were fabricated by LT-MBE, and their magnetic and transport properties were characterized. It has been demonstrated that the magnetic coupling between two ferromagnetic layers can be controlled by tuning the thickness and/or the barrier hight of the non-magnetic layer. Furthermore, we have observed the giant magnetoresistance effect in this system for the first time. Less