Study of Point Defects in Semiconductors using Optical Detection of Magnetic Resonance

9704386沃特金斯这个实验研究项目集中在技术上相关的半导体中存在的原子尺度缺陷，通过磁共振的光学检测和光学检测的电子-核双共振来探测。这些缺陷包括空位、间隙和反位等本征缺陷，以及重要的化学杂质和它们之间相互作用产生的简单络合物。研究的目的是了解这类缺陷的基态、亚稳态和激发态的电子和振动结构，并在微观尺度上确定它们在这类材料的电子和光学性质中所起的作用。新的研究重点放在宽禁带半导体上，包括II-VI化合物、III-V氮化物、金刚石和碳化硅。其基本原理是，人们对这些材料中的缺陷知之甚少，有充分的理由预计它们的性质会出现意外和新的重要物理现象。这是因为一方面从带隙获得的复合能增加，另一方面由于更大的电子局域化而增加了多电子效应的作用。在处理深层次缺陷时，理论是紧迫的，高质量的实验信息将有助于指导和检验新的理论。此外，这些材料具有潜在的可见光、紫外光发射和高温电子器件的技术价值。这样的应用将需要对点缺陷的了解，远远超出了目前所知的很少。一个主要的实验方法是用2.5 MeV的电子辐照产生本征缺陷，以便用ODMR和ODENDOR技术进行研究。在某些情况下，在一个特殊的ODMR设备中，4.2K的原位照射将允许在低温和缓慢升温的情况下研究原始的Frenkel对缺陷(空位-间隙紧密对)。这个实验项目的重点是出现在半导体晶体样品中的重要原子级缺陷结构。众所周知，这些缺陷包括空位晶格、位于间隙位置的额外原子和化学取代(例如作为硅中的杂质)对半导体的电子性质有重要影响。像In Si这样的点缺陷引入一个额外的电子进行导电(这些被称为施主杂质)；另一些点缺陷引入空穴，当施加加速场时，所有的点缺陷都对电子和空穴的运动产生“散射”效应，在给定的电压下倾向于减小电流。本项目利用先进的光学检测磁共振方法来研究各种点缺陷。这项工作将集中在那些正在考虑用于硅和砷化镓不适合的独特应用的“宽禁带”半导体上。宽禁带半导体可能用于可见光和紫外光发光二极管以及高温电子器件。感兴趣的半导体包括，例如，碳化硅和氮化镓。实验工作的一个特殊方面将是故意通过电子辐照引入点缺陷。这项工作涉及一名博士后研究员，他将在这项研究过程中接受出色的培训，以便在工业、政府或学术界担任职位。***

9704386 Watkins This experimental research project centers on the atomic scale defects present in technologically relevant semiconductors as probed by optical detection of magnetic resonance and by optically detected electron-nuclear double resonance. The defects of interest include intrinsic defects such as vacancies, interstitials and anti-sites, as well as important chemical impurities and simple complexes resulting from interactions between them. The purpose of the research is to understand the electronic and vibronic structure of the ground, metastable, and excited states of such defects, and to determine on a microscopic scale the role they play in the electronic and optical properties of this class of materials. The emphasis in the renewed research is toward the wide bandgap semiconductors, including II-VI compounds, III-V nitrides, diamond, and SiC. The rationale is that relatively little is known about the defects in these materials and there is good reason to anticipate surprises and new important physics in their properties. This is because of competition between the increased recombination energy available from the bandgap on the one hand, and the increased role of many- electron effects due to the greater electronic localization on the other. Theory is pressed in dealing with deep defects, and high quality experimental information will be useful to guide and test new theory. In addition, these materials are of technological interest for their potential as visible and uv light emitting and high temperature electronic devices. Such applications will require an understanding of point defects greatly in excess of what little is now known. A major experimental approach will be to produce intrinsic defects by 2.5MeV electron irradiation for study by the ODMR and ODENDOR techniques. In some cases irradiation in situ at 4.2K in a special ODMR facility will allow study of pristine Frenkel pair defects (vacancy-interstitial close pairs) at low temper ature and as they are slowly warmed. %%% This experimental project focuses on important atomic scale defect structures that occur in crystalline samples of semiconductors. Such defects, which include vacant lattice sites, additional atoms located interstitially, and chemical substitutions (as for example As as an impurity in Si) are well known to have important consequences on the electronic properties of semiconductors. Such point defects as As in Si introduce an extra electron for electrical conduction (these are called donor impurities); others introduce holes, and all point defects have a "scattering" effect on the motion of electrons and holes when an accelerating field is applied, tending to reduce the current for a given voltage. The present project makes use of an advanced optically detected magnetic resonance method for study of various point defects. The work will focus on those "wide bandgap" semiconductors which are now being considered for unique applications for which silicon and gallium arsenide are not suitable. Possible applications of the wide bandgap semiconductors are for visible and ultraviolet light emitting diodes and for high temperature electronic devices. The semiconductors of interest include, for example, SiC and GaN. A special aspect of the experimental work will be deliberate introduction of point defects by electron irradiation. This work involves a postdoctoral fellow who will be excellently trained in the course of this research for a position in industry, government, or academia. ***