Optical and Far Infrared Studies of Semiconductor Heterostructures

该项目包括三个部分，它们都涉及半导体异质结构，其性质几乎完全由电子自旋决定。(1)制备并研究了通过在CdSe/ZnSe量子点体系中引入Mn而形成的自组装磁性半导体量子点。这项工作将集中于对自组装过程的理解和控制，重点是形貌、组成的一致性和对锰掺入的控制。光学研究将集中在零维系统中的交换相互作用，量子点几何中磁性近邻数目减少的影响，以及确定此类系统中(预期非常长)的自旋寿命。(2)制作和进行铁磁半导体及其多层膜的光学研究。在III-Mn-V合金中发现铁磁性是一项重大突破，它为将巨大的自旋相关效应集成到基于III-V的电子学和光电子学中提供了可能性。通过一系列的分子束外延生长III-V基铁磁体的策略，可以解决在III-V晶格中引入Mn时形成的大量缺陷密度的问题。这些系统的光学测试将特别关注通过减少缺陷和优化p型掺杂来提高这些材料的光学质量。(3)研究了基于稀磁半导体(DMS)多层膜的布拉格限制系统。这些系统提供了调谐(通过外加磁场)组成层材料之间的相对带状排列的可能性。这种可调谐性可以用来控制结构中电子和/或空穴的德布罗意波长，从而调节它们的布拉格局域。由于在基于DMS的系统中，Bragg局部化的可调性是特定于自旋的，因此该程序中开发的结构将作为自旋过滤设备的原型，这可能会在基于自旋的电子设备中找到重要的应用。这项研究将为研究生提供纳米科学和自旋电子学领域的培训，从而满足美国在这两个重要且快速发展的技术领域的人力需求。传统半导体电子学完全基于电子电荷及其对施加的电信号的响应。然而，电子还具有另一种性质：自旋。最近的实验表明，后一种性质具有一定的优势，这使得基于自旋的纳米结构成为下一代电子设备的候选者。尽管人们已经可以预见基于自旋的电子学(“自旋电子学”)在探测器系统、超快开关和量子计算中的未来应用，但在这些设备成为现实之前，许多根本问题需要解决。这项研究涉及三个相互关联的领域，涉及半导体异质结构，其性质几乎完全由电子自旋决定：自旋电子学材料的控制制备，这些材料的光学表征，以及有效识别不同自旋态的技术的发展。这些任务的圆满完成将对科学理解自旋电子学过程及其在实际技术设备中的应用做出重大贡献。这项研究将与研究生和博士后研究助理一起进行。他们将接受纳米科学和自旋电子领域的培训，为进入科学和技术工作大军做准备。***

The project consists of three parts, all of them involving semiconductor heterostructures whose properties are determined almost entirely by electron spin. (1) Fabricate, and carry out optical studies of self-assembled magnetic semiconductor quantum dots (QDs) achieved by introducing Mn into the CdSe/ZnSe QD system. This effort will focus on the understanding and control of the self-assembly process, with emphasis on the morphology, uniformity of composition, and control of Mn incorporation. Optical studies will concentrate on the exchange interaction in zero-dimensional systems, on the effect of a reduced number of magnetic nearest-neighbors in the QD geometry, and on determining the (expectedly very long) spin lifetimes in such systems. (2) Fabricate and perform optical studies of ferromagnetic semiconductors and their multilayers. The discovery of ferromagnetism in III-Mn-V alloys is a major breakthrough that holds out possibilities of integrating giant spin-related effects into III-V-based electronics and optoelectronics. The problem of the large density of defects that form when Mn is introduced into the III-V lattice will be addressed by a series of strategies for MBE growth of III-V based ferromagnetics. Optical tests of these systems will focus specifically on improving the optical quality of these materials via defect reduction and optimization of p-type doping. (3) Bragg-confining systems based on diluted magnetic semiconductor (DMS) multilayers will be investigated. These systems offer the possibility of tuning (via an applied magnetic field) the relative band alignment between the constituent layer materials. This tunability can be used for controlling the de Broglie wavelength of electrons and/or holes within the structure, and thus for tuning their Bragg localization. Since in DMS-based systems the tunability of Bragg localization is spin-specific, the structures developed in the program will serve as prototypes for spin-filtering devices that may find important application in spin-based electronics. This research will provide training for graduate students in areas of nanoscience and spin-based electronics, thus meeting U.S. manpower needs in two important and rapidly developing areas of technology.%%% Traditional semiconductor electronics is based entirely on the electron charge and its response to applied electric signals. The electron, however, is also characterized by another property: the spin. Recent experiments have demonstrated that this latter property holds out certain advantages which make spin-based nanostructures attractive as candidates for the next generation of electronic devices. Although one can already envision future applications of spin-based electronics ("spintronics") in detector systems, ultra-fast switches and quantum computing, many fundamental issues need to be resolved before such devices can become reality. This research deals with three inter-related areas involving semiconductor heterostructures whose properties are determined almost entirely by electron spin: Controlled fabrication of spintronics materials, optical characterization of these materials, and development of techniques for the effective identification of different spin states from one another. Successful completion of these tasks will be major contributions to the scientific understanding of spintronics processes and their incorporation in practical technological devices. This research will be performed with graduate students and postdoctoral research associates. They will receive training in areas of nanoscience and spin-based electronics in preparation for their entry into the scientific and technological workforce. ***