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

该提案是根据21世纪自旋电子学倡议，项目招标NSF 02-036收到的。本文主要研究了磁性半导体量子阱结构和磁隧穿二极管界面上的自旋相关输运和磁现象，这些现象在自旋电子学中具有强大的应用前景。由于这些异质结构中的界面似乎对器件特性起着至关重要的作用，因此需要详细研究电子和磁性界面特性以及跨异质结的分裂输运。我们的实验计划的目的是解决有关自旋散射，磁态和手对准在埋藏异质界面的基本问题。将研究化合物形成（混合）、粗糙度、磁态和缺陷的影响，并将其与生长条件、结构性质和磁输运测量相关联。利用飞秒分辨泵浦探针线性和非线性磁光实验测量自旋寿命和退相干时间，以阐明埋藏异质界面处的自旋散射和自旋弛豫过程。电（通过光导开关）和光注入（使用线性和圆偏振超快脉冲）将被用来激发自旋种群。内部光电发射实验（圆偏振）将被用来绘制自旋手在异质结处的排列。采用表面敏感磁致二次谐波（MSGH）技术测量埋地界面处的磁化动力学。将进行MSGH光谱研究以揭示界面态，这些界面态可能作为异质结的自旋散射中心。这些测量将根据以下因素进行：温度、外加磁场、外加偏压、成分、井厚和/或载波高度、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焦点将是对新生的自旋电子学领域的研究生和本科生的教育。学生将受益于拟议的研究计划，为他们提供跨学科领域的优秀培训，包括光学和电子材料与器件。

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.