Charge Transport in the Impurity Band of Dilute Magnetic Semiconductors: Experiment and Theory

通过将磁性原子掺入常规掺杂的半导体中，人们进入了磁学和半导体物理学之间的一个有趣的领域。一方面，在稀磁半导体中，如Zn1-xMnxSe：CL中，电子结构上的自旋效应可以通过改变x连续地调节到数量级。另一方面，通过改变施主浓度ND，Cl-施主能级演化为所谓的杂质带(IB)，为验证固体介质中电荷输运的基本物理概念提供了一个很好的实验基础。与非磁性系统相比，DMS表现出非常不同的传输行为。这适用于金属-绝缘体转变(MIT)两侧的两个区域--低施主浓度下的跳跃电导率和高掺杂水平下的金属电导率。这些差异必然源于散射过程中增强的自旋效应的相互作用，施主波函数的形状，以及杂质和导带的态密度随自旋的变化。然而，传统的模型不能解释观察到的行为。大多数电荷输运理论只适用于非磁性系统，假定杂质能级是自旋简并的，与外加磁场无关。我们将对不同系列的n型Zn1-xMnxSe进行低温磁输运和磁光光谱测量，这是一个理想的模型体系，因为x和ND的浓度可以独立变化。实验研究将与充分输运理论的发展相结合，以模拟实验结果，从而阐明DMS中电荷输运和MIT的基本问题。

By incorporating magnetic atoms into conventionally doped semiconductors one enters an interesting field between magnetism and semiconductor physics. On the one hand, in dilute magnetic semiconductors (DMS) such as Zn1-xMnxSe:Cl, spin-effects on the electronic structure can be tuned continuously up to orders of magnitude by varying x. On the other hand, the evolution of the Cl-donor energy levels into a so called impurity band (IB) by varying the donor concentration ND provides an excellent test-ground for verifying fundamental physical concepts of charge transport in solid media. DMS show a very different transport behavior compared to non-magnetic systems. This holds for both regimes on either side of the metal-insulator transition (MIT) – hopping conductivity at low donor concentrations and metallic conductivity at high doping levels. These differences must arise from the interplay of enhanced spin effects in the scattering processes, in the shape of the donor wave functions, and in the spin-dependent changes of the density of states of impurity and conduction bands. However, conventional models cannot account for the observed behavior. Most theories of charge transport are applicable only to non-magnetic systems assuming that the impurity levels are spin-degenerate and independent of external magnetic field. We will perform low-temperature magneto-transport and magneto-optical spectroscopic measurements on different series of n-type Zn1-xMnxSe, which is an ideal model system as concentrations x and ND can be varied independently. The experimental study will be combined with the development of an adequate transport theory to model the experimental results and, thus, to clarify the fundamental problems of charge transport and MIT in DMS.