Magnetic Moments in Amorphous Semiconductors

技术解释 本项目将研究在半导体中加入磁矩对所得材料的电磁特性的影响。重点将放在非晶半导体上，在那里可以很容易地引入各种各样的掺杂剂，而不会破坏结构。非晶硅，锗，和各种形式的C掺杂的磁性离子，如稀土元素，铁和锰将制备和它们的电子，磁性，热力学和结构性能的测量。声子刚度和半导体带隙对这些属性的影响将被确定。在无定形C中，键合可以并且将从石墨到类金刚石变化，允许带隙从接近零到大。我们将研究附加的局域磁矩和在金属-绝缘体转变时电子局域化时形成的自发磁矩之间的相互作用。该研究将为三维金属-绝缘体转变的微观模型提供唯象基础，并了解将局部磁矩引入半导体对输运和磁性的影响。该项目将为两名研究生和大约5-6名本科生提供研究培训和教育，包括通过PI与磁记录行业以及国家高磁场实验室和劳伦斯伯克利实验室的合作接触行业和国家实验室。非技术性解释故意增加磁性或“磁矩”到半导体产生的影响是非常大的。特别地，当这种材料被放置在磁场中时，电阻的变化（磁阻）可能是巨大的。该项目将研究将磁性原子添加到非晶（非晶体）半导体Si，Ge和C中的效果，故意创造和研究以前没有制造的新材料。将制备掺杂有磁性离子如稀土元素、Fe和Mn的非晶Si、Ge和C的膜。它们的电子，磁性，热力学和结构特性将在很宽的温度，磁场和掺杂水平范围内进行测量。这项研究将试图确定半导体中磁矩大效应的原理。对这些效应的进一步理解可能会为开发利用电子的磁特性（除了其电荷之外，还包括其“自旋”，即自旋电子学）的技术提供非常大的磁阻。此外，这项研究旨在增加我们对磁矩在当前感兴趣的材料（如高温超导体）中发挥如此关键作用的理解。该项目将为研究生和本科生提供研究培训和教育，并通过合作为他们提供行业和国家实验室的机会。因此，学生将为未来在学术界，工业或政府实验室的职业生涯做好准备。

TECHNICAL EXPLANATION This project will investigate the effect of adding magnetic moments to semiconductors on the electrical and magnetic properties of the resultant materials. The focus will be on amorphous semiconductors where a wide variety of dopants can be readily introduced without damaging the structure. Amorphous Si, Ge, and various forms of C doped with magnetic ions such as rare earth elements, Fe and Mn will be prepared and their electronic, magnetic, thermodynamic, and structural properties measured. The influence of the phonon stiffness and the semiconductor band gap on these properties will be determined. In amorphous C, the bonding can and will be varied from graphitic to diamond-like, allowing the band gap to be tuned from near zero to large. The interaction between the added local moments and the spontaneous moments formed at the Metal-Insulator transition as electrons localize will be studied. The research will provide a phenomenological underpinning for a microscopic model for the three dimensional Metal-Insulator transition, and an understanding of the effect on both transport and magnetic properties of introducing local magnetic moments into a semiconductor. The project will provide research training and education for two graduate students and an estimated 5-6 undergraduates, including exposure to industry and to the national laboratories through the PI's collaborations with the magnetic recording industry and with the National High Magnetic Field Lab and Lawrence Berkeley Lab. NON-TECHNICAL EXPLANATIONThe deliberate addition of magnetism or "magnetic moments" to semiconductors produces effects that are extremely large. In particular the change in the electrical resistance when such a material is placed in a magnetic field (magnetoresistance) can be enormous. This project will investigate the effect of adding magnetic atoms to amorphous (non-crystalline) semiconductors Si, Ge, and C, deliberately creating and studying new materials not previously made. Films of amorphous Si, Ge, and C doped with magnetic ions such as rare earth elements, Fe, and Mn will be prepared. Their electronic, magnetic, thermodynamic, and structural properties will be measured over a wide range of temperature, magnetic field, and doping levels. The research will attempt to determine the principles governing the large effect of magnetic moments in semiconductors. An increased understanding of these effects may point the way to making the very large magnetoresistance of use to a developing technology that will use the magnetic property of the electron, its "spin" in addition to its charge, i.e. spin electronics. In addition this research aims to increase our understanding of why magnetic moments play such a crucial role in materials of current interest, such as the high temperature superconductors. The project will provide research training and education for graduate and undergraduate students, and provide them with an exposure to industry and to the national labs through collaborations. Thus, the students will be well prepared for future careers in academia, or industrial or government laboratories.