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

由稀释磁性半导体（DMS）和非磁性半导体组成的人工异质结构，如CdTe/Cd_<1-x>Mn_xTe超晶格（SLs），在SL势中量子化的电子态被仅发生在DMS层的交换相互作用所改变。换句话说，CdTe/Cd_<1-x>Mn_xTe SLs的电子性质可以通过施加磁场通过DMS层的巨大塞曼分裂（塞曼调谐）来调谐。在本研究中，研究了CdTe/Cd_<1-x>Mn_xTe多量子阱（mqw）的磁光性质，重点研究了以下两个主题。a)磁场诱导的I-type - II型转变我们研究了Mn浓度相对较大（约0.3）的mqw的I-type - II型转变。在这种价带偏移较大的mqw中，类型跃迁预计会在非常高的磁场下发生。然后我们测量了单匝线圈技术产生的高达150 T脉冲磁场下的磁吸收光谱。结果，我们发现了与类型转换相关的明显特征-吸收强度减小和重空穴激子能量红移的开始。当价带偏移比假设为30-40%时，通过变分计算可以很好地再现这些观察到的特征。b)磁光研究异质界面的展宽。在实际的单晶硅异质界面中，总是存在着展宽的现象，跨界面的成分变化不是完全突然的，而是由于晶体生长的各种过程而展宽的。这种界面展宽有望增强CdTe阱层中激子的巨大塞曼分裂，因为展宽区域的磁化强度比Cd_<1-x>Mn_xTe层的磁化强度大。因此，从观察到的塞曼分裂可以通过与模型计算的比较来估计界面展宽的程度。我们研究了在不同生长条件下生长的MQW样品的界面展宽程度，如II/VI元素的通量比、衬底温度和生长后的热退火。结果发现，在Cd或Te通量超标的情况下进行MBE生长，其展宽长度对衬底温度的依赖性不同。由此推断，在te过量生长时，界面展宽是由Cd和Mn原子的热扩散引起的，而在Cd过量生长时，界面展宽是由偏析引起的。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