Control and application of magneto-optical properties in semicondoctor superlattices including magnetic elements

在由稀磁半导体（DMS）和非磁半导体（如CdTe/Cd_<1-x>Mn_xTe超晶格）组成的人工异质结构中，仅在DMS层中发生的交换作用改变了在SL势中量子化的电子态。换句话说，<1-x>通过施加磁场，可以通过DMS层的巨大塞曼分裂（Zeeman tuning）来调谐CdTe/Cd_ Mn_xTe超晶格的电子性质。本研究主要研究了CdTe/Cd_<1-x>Mn_xTe多量子威尔斯（MQW）的磁光性质，重点研究了以下两个问题：a）磁场诱导的I型-II型转变我们研究了具有相对较大的Mn浓度（约0.3）的MQW中的I型-II型转变。在这样的多量子阱与大的价带偏移，类型的转变预计将发生在非常高的磁场。然后测量了在高达150 T的脉冲磁场下的磁吸收谱 关于我们 通过单匝线圈技术。结果表明，我们发现了与吸收强度的类型转变减小和重空穴激子能量的红移有关的明显特征。b）异质界面加宽的磁光研究在实际超晶格的异质界面中，总是存在加宽现象，即由于晶体生长过程中的各种原因，界面上的组分变化不是完全突变的，而是加宽的。这种界面加宽将增强CdTe阱层中激子的巨大塞曼分裂，因为加宽区的磁化强度大于Cd_<1-x>Mn_xTe层的磁化强度。因此，从观察到的塞曼分裂的程度，界面加宽可以估计通过比较它与模型计算。我们研究了在不同生长条件下生长的多量子阱样品的界面加宽程度，如II/VI族元素的流量比，衬底温度和生长后的热退火。结果发现，在Cd或Te通量过量的情况下进行MBE生长，加宽长度对衬底温度的依赖性是不同的。由此推断，Te过量生长时，界面加宽是由Cd和Mn原子的热扩散引起的，Cd过量生长时，界面加宽是由偏析引起的。少

Artificial heterostructures consisting of diluted magnetic semiconductors (DMS) and non-magnetic semiconductors, such as CdTe/Cd_<1-x>Mn_xTe superlattices (SLs), electronic states quantized in the SL potential are modified by the exchange interaction which takes place only in the DMS layr. In other words, electronic properties of CdTe/Cd_<1-x>Mn_xTe SLs can be tuned by applying magnetic fields through the gigantic Zeeman splitting of DMS layr (Zeeman tuning). In this study, the magneto-optical properties of CdTe/Cd_<1-x>Mn_xTe multiple quantum wells (MQWs) were investigated with a special emphasis on the following two topics.a) Magnetic-field induced type I-type II transitionWe studied the type I-type II transition in MQWs with relatively large Mn concentration of about 0.3. In such MQWs with large valence-band offset, the type transition is expected to take place at very high magnetic fields. Then we measured magneto-absorption spectra under pulsed magnetic fields up to 150 T produced … More by the single-turn coil technique. As a result, we found evident features associated with the type transition-diminution of the absorption intensity and the onset of a red-shift of the heavy-hole exciton energy. These observed features were reproduced qualitatively well by a variational calculation when valence-band offset ratio is assumed to be 30-40%.b) Magneto-optical study of broadening at the heterointerfaceIn the heterointerface of an actual SLs, there always exists broadening-the change of composition across the interface is not parfectly abrupt but broadened owing to various process in the crystal growth. This interface broadening is expected to enhance the gigantic Zeeman splitting of the exciton confined in the CdTe well layr, because the magnetization of the broadened region becomes larger than that of the Cd_<1-x>Mn_xTe layr. Therefore from the observed Zeeman splitting the degree of the interface broadening can be estimated by comparing it with a model calculation. We investigated the degree of the interface broadening in MQW samples grown at various growth conditions, such as flux ratio of II/VI elements, substrate temperatures and thermal annealing after the growth. As a result, it was found that the dependence of the broadening lengths on the substrate temperature is different according as the MBE growth was performed in the excess of Cd or Te flux. From this it is deduced that the interface broadening is caused by the thermal diffusion of Cd and Mn atoms in the case of Te-excess growth and is caused by the segregation in the case of Cd-excess growth. Less