RUI: Measurement of Density of States of (Ga,Mn)As and Diffusion of Photoinduced Order by Ultrafast Transient-Grating Spectroscopy

RUI：超快瞬态光栅光谱测量 (Ga,Mn)As 态密度和光致有序扩散

• 批准号: 1105553
• 负责人: Christopher Weber
• 金额: $ 19万
• 依托单位: Santa Clara University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-01 至 2015-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1105553&HistoricalAwards=false
• 关键词: RUI; Measurement; Density; States; Ga

****Technical Abstract****(Ga,Mn)As is the best-studied of the III-V dilute magnetic semiconductors (DMS). These materials offer possible spintronic applications through the optical and electrical control of their magnetic properties, but practical application awaits the design of new materials with Curie temperature above room temperature. The Einstein relation allows one to find the density of states at the Fermi level (DOS) based on measurements of the resistivity and the hole diffusion coefficient, independent of hole density. This project will use ultrafast optics to measure the hole diffusion coefficient, and thereby determine the DOS. The experiment will apply transient-grating spectroscopy to (Ga,Mn)As, thus measuring the spin diffusion and the ambipolar diffusion; these two in turn, give the hole diffusion. These measurements could distinguish between the widely supported valence-band and impurity-band pictures of holes in (Ga,Mn)As. Since the holes mediate magnetic exchange, the debate over their properties is fundamental to understanding DMS's, and improved understanding could aid the development of new DMS materials. Undergraduate students will participate in every part of the project. They will learn about ultrafast lasers, optical alignment, data analysis, magnetism, semiconductor physics, and spectroscopy. The experience will prepare them for a wide variety of careers and graduate programs.****Non-Technical Abstract****The dilute magnetic semiconductors (DMS's) become magnetic when they are "doped" with small quantities of impurities. Magnetic semiconductors could be used in many proposed devices, including nonvolatile transistors that would dramatically reduce computers' power consumption, but practical use will require the design of new DMS materials that operate at room temperature, rather than the subzero temperatures of current materials. The search for such materials has suffered from a lack of theoretical understanding of how a DMS becomes magnetic. GaMnAs is an archetypal DMS, but there is sharp disagreement over the electronic processes that make it magnetic, particularly over how mobile the "holes" are that control its magnetism. This project will use ultrafast lasers, with pulses shorter than one ten-trillionth of a second, to measure the holes' mobility, providing an improved understanding of DMS's. The project will also investigate a related phenomenon, as yet poorly understood, in which exposure to light strengthens the magnetism of GaMnAs. Undergraduate students will participate in every part of the project, contributing to experimental progress and being trained in experimental physics. They will learn to use ultrafast lasers, get very good at optical alignment, and become familiar with magnetism, semiconductor physics, and spectroscopy. Because of the scientific and industrial relevance of these topics, and the rapid growth of ultrafast technology, the students will be prepared for a wide variety of careers and graduate programs.

* 技术摘要 *（Ga，Mn）As是III-V族稀磁半导体中研究最多的一种。这些材料通过光学和电学控制其磁性提供了可能的自旋电子应用，但实际应用还需要设计居里温度高于室温的新材料。爱因斯坦关系允许人们基于电阻率和空穴扩散系数的测量来找到费米能级（DOS）处的态密度，而与空穴密度无关。本计画将利用超快光学来量测电洞扩散系数，进而决定掺杂浓度。实验将应用瞬态光栅光谱（Ga，Mn）As，从而测量自旋扩散和双极扩散;这两个反过来，给出了空穴扩散。这些测量可以区分广泛支持的（Ga，Mn）As中空穴的价带和杂质带图像。由于空穴介导了磁交换，因此对其性质的争论对于理解DMS是至关重要的，并且改进的理解可以帮助开发新的DMS材料。本科生将参与项目的每一部分。他们将学习超快激光，光学对准，数据分析，磁学，半导体物理和光谱学。这些经验将使他们为各种各样的职业和研究生课程做好准备。非技术摘要 * 稀磁半导体（DMS）在“掺杂”少量杂质时变得具有磁性。磁性半导体可以用于许多拟议的设备，包括非易失性晶体管，这将大大降低计算机的功耗，但实际使用将需要设计在室温下工作的新DMS材料，而不是当前材料的零度以下温度。对这种材料的研究一直缺乏对DMS如何变得磁性的理论理解。GaMnAs是一种典型的DMS，但在使其具有磁性的电子过程上存在尖锐的分歧，特别是在控制其磁性的“空穴”的移动的程度上。该项目将使用超快激光器，脉冲短于十万亿分之一秒，以测量空穴的迁移率，提供对DMS的更好理解。该项目还将研究一个相关的现象，但目前还不清楚，其中暴露在光下会增强GaMnAs的磁性。本科生将参与项目的每一部分，为实验进展做出贡献，并接受实验物理方面的培训。他们将学习使用超快激光，在光学对准非常好，并熟悉磁性，半导体物理和光谱学。由于这些主题的科学和工业相关性，以及超快技术的快速发展，学生将为各种各样的职业和研究生课程做好准备。