Isotopically Controlled Semiconductors: Diffusion and Nanocrystals

*非技术摘要*这个项目将解决两个具有重大科学和技术意义的半导体问题。第一个问题与半导体中杂质在高温下的精确运动有关，这种运动是由一种称为扩散的过程引起的。在标准硅片上生长的混合晶层会产生机械应力，进而影响载流子迁移率和掺杂扩散。应对这些影响进行定量研究和测定，以充分发挥晶体合金化的潜力。这一研究结果将有助于形成更小、更快的集成电路。第二个项目的重点是半导体纳米晶。为了使半导体具有特殊的导电性能，通常要添加其他元素的原子。这个过程被称为掺杂半导体，添加的原子被称为掺杂剂。掺杂纳米晶体是具有挑战性的，因为掺杂原子会移动到附近的纳米晶体表面，在那里它们不再像预期的那样发挥作用。中子嬗变掺杂(NTD)将被用来通过热神经元捕获和放射性衰变将一些半导体原子转变为掺杂剂。NTD过程可以在室温下进行，在那里掺杂剂被冻结？取代他们的位置。如果成功，应用于纳米晶体的NTD工艺可能导致晶体管和二极管的最终微型化。在本科生的帮助下，研究生将完成所有描述的研究。这项以发现为导向的研究将获得硕士和博士学位，保持一支训练有素的劳动力队伍，这对美国的竞争力至关重要。*技术摘要*集成电路的性能可以通过施加机械应力来提高电子和空穴的迁移率来提高。生长的SiGe合金外延层会产生必要的应力。该项目将利用同位素控制、应力以及松弛的Si(1-x)Ge(X)多层结构来确定主要掺杂物：硼、砷和磷的扩散系数和扩散机制。二次离子质谱学将是确定掺杂物和基质晶体原子深度分布的主要工具。所得信息将对先进半导体器件的设计和制造有所帮助。该项目的第二个重点是Ge和Si纳米晶的掺杂，这是一个由于分离到附近表面而造成的严重问题。70Ge或74Ge等具有蠕变特性的纳米晶体的中子嬗变掺杂(NTD)过程使冷？通过热中子俘获和放射性衰变进行掺杂：70Ge n产生受主71Ga；而74Ge n产生施主75As。假设核-壳、双叶和合金化纳米晶的形成是可控制的，那么可以预见到丰富的掺杂结构。攻读硕士和博士学位的研究生将在本科生的帮助下进行实验研究。这种半导体科学和技术前沿的培训有助于维持国内的专家队伍，这对美国的工业竞争力至关重要。

****NON-TECHNICAL ABSTRACT****This project will address two semiconductor issues of great scientific and technological interest. The first one relates to the precise motion of impurities in semiconductors at high temperatures caused by a process called diffusion. Mixed crystal layers grown on standard silicon wafers generate mechanical stress, which in turn affects carrier mobility and dopant diffusion. These effects shall be studied and determined quantitatively so that the full potential of crystal alloying can be reached. The results of this study will benefit the formation of smaller and faster integrated circuits. The second project focuses on semiconductor nanocrystals. To make a semiconductor have particular conducting properties, atoms of other elements are often added. This process is known as doping the semiconductor, and the added atoms are called ?dopants.? Doping nanocrystals is challenging because dopant atoms move to the nearby nanocrystal surface where they no longer function as expected. Neutron Transmutation Doping (NTD) will be used to transform some of the semiconductor atoms into dopants via thermal neuron capture followed by radioactive decay. The NTD process can be performed at room temperature where the dopants are ?frozen? in their place. If successful, the NTD process applied to nanocrystals may lead to the ultimate miniaturization of transistors and diodes. Graduate students assisted by undergraduates will perform all the research described. The discovery-oriented research will lead to Masters and Ph.D. degrees, maintaining a highly trained workforce, which is crucial for US competitiveness.****TECHNICAL ABSTRACT****The performance of Integrated Circuits can be improved by raising the electron and hole mobilities through the application of mechanical stress. Growing epitaxial layers of SiGe alloys can induce the necessary stress. This project will make use of isotopically controlled, stressed as well as relaxed Si(1-x)Ge(x) multilayer structures to determine the diffusivities and diffusion mechanisms of the major dopants; Boron, Arsenic and Phosphorus. Secondary Ion Mass Spectroscopy will be the main tool to determine the depth distribution of dopants and host crystal atoms. The resulting information will be useful in the design and fabrication of advanced semiconductor devices. A second focus of the project is the doping of Ge and Si nanocrystals, a formidable problem caused by segregation to the nearby surface. The Neutron Transmutation Doping (NTD) process of istopically enriched nanocrystals such as 70Ge or 74Ge makes possible ?cold? doping via thermal neutron capture followed by radioactive decay: 70Ge + n produces the acceptor 71Ga; while 74Ge + n produces the donor 75As. A rich range of doped structures can be envisioned assuming the formation of core-shell, bi-lobe and alloyed nanocrystals can be controlled. Graduate students working towards their MS and Ph.D. degrees will conduct the experimental research assisted by undergrads. This training at the cutting edge of semiconductor science and technology contributes to the maintenance of a domestic pool of experts, which are vital for the U.S. industrial competitiveness.