Fabrication and Study of Nanostructure Diluted Magnetic Semiconductors

本研究计划的目的是制备由稀磁半导体（DMSs）组成的新型纳米结构晶格，并研究纳米结构的磁光特性。为此，我们利用分子束外延、原子束外延和电子束光刻技术制备了二维量子威尔斯、一维量子线和零维量子点。我们制备了<1-x><1-x>Mn浓度为x= 0.03- 0.3的Cd_ Mn_xTe和Cd_ Mn_xSe材料。利用<1-x>量子阱激子态的选择性激发，测量了Cd_ Mn_xTe量子阱威尔斯的时间分辨光致发光。激子发光的瞬态行为清楚地显示了激子磁极化子的形成过程，而强外磁场对激子磁极化子的形成有抑制作用。在<1-x>ZnSe缓冲层上用Stranski-Krastanow模式生长的Cd_ Mn_xSe量子点中激子的衰减非常快。量子点激子的寿命被外磁场显著增加。解释的现象是由于激子波函数的磁场收缩的非辐射过程的减少。在Cd_ Mn_xTe量子阱上进行了泵浦-探测瞬态吸收光谱研究<1-x>，在2 ps-3 ns时间范围内观察到激子和磁极化子的动力学过程。Zn_<1-x>Cd_xSe系统量子线的光致发光显示了一维限制效应以及通过减小线宽使晶格应变弛豫的证据。Cd_<1-x>Mn_xSe量子线的制备正在进行中，本项目所揭示的纳米结构DMS的显著磁光效应将促进新型磁光微器件的研究。

The objective of this research project is to fabricate new nanostructure lattices composed of diluted magnetic semiconductors (DMSs) and also to study magneto-optical properties of the nanostructures. For this purposes, we have fabricated 2-dimensional quantum wells, 1-dimensional quantum wires, and 0-dimensional quantum dots by molecular beam epitaxy, atomic beam epitaxy, and electron-beam lithography techniques. Materials we have fabricated are Cd_<1-x>Mn_xTe and Cd_<1-x>Mn_xSe with Mn concentration of x= 0.03-0.3.Obtained these nanostructures have been studied by the ultrafast laser spectroscopy using femto-second pulse lasers. Time resolved photoluminescence has been measured in Cd_<1-x>Mn_xTe quantum wells by the selective excitation of the quantum-well exciton states. The transient behavior of the exciton luminescence clearly shows the formation process of the excitonic magnetic polarons, which is suppressed by the strong external magnetic fields. Quantum dots of Cd_<1-x>Mn_xSe grown by the Stranski-Krastanow mode on ZnSe buffer layers show very fast decay of the excitons in the dots. The lifetime of the quantum dot excitons is markedly increased by the external magnetic fields. The phenomena are interpreted by decrease of the nonradiative process due to the shrinkage of the exciton wavefunction by the magnetic field. Pump-probe transient absorption spectroscopy has been made on Cd_<1-x>Mn_xTe quantum well, The exciton and magnetic polaron dynamics are observed in the 2 ps to 3 ns time region. Quantum wires of Zn_<1-x>Cd_xSe system show the photoluminescence evidence of the 1-dimensional confinement effect as well as the relaxation of the lattice strains by decreasing the wire width. Fabrication of Cd_<1-x>Mn_xSe quantum wires is under progress.The remarkable magneto-optical effects of the nanaostructure DMSs elucidated in the present project will stimulate the research of the new magneto-optical microdevices.