Fabrication and Study of Nanostructure Diluted Magnetic Semiconductors

本研究项目的目的是制备由稀磁半导体(DMS)组成的新型纳米结构晶格，并研究其磁光性质。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阱、一维量子线和零维量子点。我们制备的材料是Cd_&lt；1-x&gt；Mn_xTe和Cd_&lt；1-x&gt；Mn_xSe，其中x=0.03-0.3。利用飞秒脉冲激光的超快激光光谱研究了这些纳米结构。通过选择激发量子井激子态，测量了Cd&lt；1-x&Gt；MnxTe量子阱中的时间分辨光致发光。激子发光的瞬时行为清楚地显示了激子磁极化子的形成过程，而激子磁极化子在强磁场的作用下受到抑制。用STranski-Krastanow模式在锌硒缓冲层上生长的Cd_(1-x)&Gt；Mn_xSe量子点的激子衰减非常快。在外加磁场的作用下，量子点激子的寿命显著增加。这些现象是由于磁场引起激子波函数的收缩而导致的非辐射过程的减少。对Cd&lt；1-x&Gt；MnxTe量子阱进行了泵浦探测暂态吸收光谱，在2ps~3 ns的时间范围内观察到了激子和磁极化子的动力学。Zn&lt；1-x&Gt；Cd_xSe体系的量子线显示出一维限制效应的光致发光证据，同时随着线宽的减小，晶格应变也发生了松弛。Cd&lt；1-x&Gt；MnxSe量子线的制备正在进行中，本项目所阐明的纳米结构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.