SPIN ELECTRONICS: Band-Offset and Time-Resolved Nonlinear-Optical Studies of Magnetic Heterostructure Interfaces

该提案是响应21世纪世纪自旋电子学倡议，计划征集NSF 02-036而收到的。 该提案的重点是磁性半导体量子阱结构和磁性隧道二极管界面处的自旋相关输运和磁性现象，这些结构在自旋电子学中具有强大的ML应用。由于这些异质结中的界面似乎对器件特性起着至关重要的作用，因此需要详细研究异质结中的电子和磁性界面特性以及分裂输运。我们的实验计划的目的是解决有关自旋散射，磁状态和手在掩埋异质界面对齐的基本问题。化合物的形成（混合），粗糙度，磁状态和缺陷的影响将进行研究，并与生长条件，结构特性和磁输运测量。自旋寿命和退相干时间将通过飞秒分辨的泵浦-探测线性和非线性磁光实验来测量，以阐明在掩埋异质界面处的自旋散射和自旋弛豫过程。电注入（通过光电导开关）和光注入（线性和圆偏振超快脉冲）都将用于激发自旋布居。内部光电发射实验（圆偏振）将被用来映射在异质结的自旋手的对齐。在掩埋界面的磁化动力学将使用表面敏感的磁化感应二次谐波产生（MSGH）技术测量。利用MSGH光谱研究了异质结中可能作为自旋散射中心的界面态。这些测量将作为以下各项的函数来执行：温度、施加的磁场、施加的电偏压、组成、阱厚度和/或势垒高度、内置应变和生长条件。从这些测量中获得的关于自旋手对准的信息可以用于调谐到共振状态，从而提高自旋注入过程的效率。我们计划的一个主要重点将是研究生和本科生在自旋电子学的新兴领域的教育。学生将从拟议的研究计划中受益，为他们提供包括光学和电子材料和设备在内的跨学科领域的优秀培训。

This proposal was received in response to the Spin Electronics of the 21st Century Initiative, Program Solicitation NSF 02-036. The proposal focuses on spin-dependent transport and magnetic phenomena at interfaces of magnetic semiconductor quantum well structures and magnetic tunneling diodes which have potent ml applications in spin electronics. As interfaces in these heterostructures appear to play an essential role for the device characteristics, a detailed study of the electronic and magnetic interface properties as well as split transport across the heterojunctions is needed. The objective of our experimental program is to resolve fundamental questions regarding spin scattering, the magnetic state and the hand alignment at the buried heterointerfaces. The effects of compound formation (intermixing), roughness, magnetic state and defects will be studied and correlated with growth conditions, structural properties and magneto-transport measurements. Spin lifetimes and decoherence times will he measured by femtosecondresolved pump-probe linear and nonlinear magneto-optical experiments to elucidate spin scattering and spin relaxation processes at the buried heterointerfaces. Both electrical (via a photoconductive switch) and optical injection (with linear and circular-polarized ultrafast pulses) will be used to excite a spin population. Internal photoemission experiments (with circular polarization) will be employed to map the alignment of the spin-hands at the heterojunctions. The magnetization dynamics at the buried interface will be measured using the surface-sensitive magnetization-induced second-harmonic generation (MSGH) technique. Spectroscopic MSGH studies will he performed to reveal interface states, which may act as spin scattering centers at the heterojunctions. These measurements will he performed as a function of: temperature, applied magnetic field, applied electrical bias, composition, well thickness and/or harrier height, built-in strain and growth conditions. The information on the spin-hand alignment obtained from these measurements can be used to tune into resonant states thereby enhancing the efficiency of the spin-injection process. A major focus of our program will be the education of graduate and undergraduate students in the nascent field of spin electronics. The students will benefit from the proposed research program, providing them with excellent training in an interdisciplinary field including optics and electronic materials and devices.