Isotopically Controlled Semiconductors: Diffusion and Nanocrystals

* 非技术摘要 * 本项目将解决两个具有重大科学和技术意义的半导体问题。 第一个与高温下半导体中杂质的精确运动有关，这种运动是由一种称为扩散的过程引起的。 标准硅晶片上生长的混合晶体层会产生机械应力，从而影响载流子迁移率和掺杂剂扩散。 应研究并定量测定这些效应，以便充分发挥晶体合金化的潜力。 本研究的结果将有利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体。 为了使半导体具有特殊的导电性能，经常添加其他元素的原子。 这个过程被称为掺杂半导体，和添加的原子被称为？掺杂剂 掺杂纳米晶体是具有挑战性的，因为掺杂剂原子移动到附近的表面，在那里它们不再像预期的那样起作用。 中子嬗变掺杂（NTD）将用于通过热神经元捕获将一些半导体原子转化为掺杂剂，然后进行放射性衰变。 NTD工艺可以在室温下进行，其中掺杂剂是？冷冻？在他们的地方。 如果成功的话，应用于纳米晶体的NTD工艺可能会导致晶体管和二极管的最终小型化。 研究生将在本科生的协助下完成所描述的所有研究。 以发现为导向的研究将导致硕士和博士学位。保持训练有素的劳动力，这对美国的竞争力至关重要。通过施加机械应力来提高电子和空穴的迁移率，可以改善集成电路的性能。 生长SiGe合金的外延层可以引起必要的应力。 该项目将利用同位素控制，应力以及松弛Si（1-x）Ge（x）多层结构，以确定主要掺杂剂的扩散率和扩散机制;硼，砷和磷。二次离子质谱将是确定掺杂剂和基质晶体原子深度分布的主要工具。 所得的信息将有助于先进半导体器件的设计和制造。 该项目的第二个重点是Ge和Si纳米晶体的掺杂，这是一个由附近表面的偏析引起的棘手问题。 同位素富集的纳米晶如70 Ge或74 Ge的中子嬗变掺杂（NTD）过程使之成为可能？冷吗通过热中子俘获掺杂，然后进行放射性衰变：70 Ge + n产生受体71 Ga;而74 Ge + n产生供体75 As。 假设可以控制核-壳、双叶和合金化纳米晶体的形成，可以设想丰富的掺杂结构范围。 攻读硕士和博士学位的研究生。学位将在本科生的协助下进行实验研究。 这种半导体科学和技术前沿的培训有助于维持国内专家库，这对美国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.