Charge Transfer in Oxide Semiconductors from a Defect's Point of View

非技术描述：今天所有的电子产品，从手机到LED，都是基于一类称为半导体的材料。 从引发计算机革命的Si等单元素材料到引发照明革命的GaN等多元素材料，半导体构成了当今电子技术的核心。被称为氧化物半导体的电子材料的子集传统上被用作气体传感器和光学窗口。然而，最近的研究表明，氧化物在电子器件应用中也具有潜力。例如，它们可以相对容易地制成大尺寸晶体，这是批量器件制造的关键因素。另一方面，控制导电性，这是一个成功的电子材料所必不可少的，是不那么容易的。因此，大部分的研究活动集中在调查潜在的令人兴奋的氧化物半导体家族固有的导电性的来源和机制。在某种程度上，所生长的氧化物晶体的高导电性是由各种类型的缺陷决定的。更好地了解这些材料中缺陷的性质、演变和相互作用，有助于确定控制缺陷所需的适当步骤，从而控制由此产生的导电性。通过参与这项研究，本科生和研究生将受益于与海军研究实验室和各种工业生产设施等领域专家的长期合作。技术说明：氧化物半导体的导电性与材料中的大量缺陷之间的关系一直是一个争论不休的问题。该研究项目旨在通过利用一种可以同时识别缺陷及其对导电性的影响的技术来研究氧化物，从而最大限度地减少争论。具体来说，这项工作调查点缺陷之间的电荷转移和固有的导电性在一个子集的氧化物半导体最相关的电子应用，即氧化锡，氧化铟和氧化镓之间的联系。所采用的方法，随时间变化的光致电子顺磁共振（光EPR），结合了磁共振的功率与时间演变的光学响应，以监测电荷转移之间的缺陷，唯一确定的EPR。时间相关数据的分析取决于从材料中的各种杂质以及晶体结构的知识开发的模型。因此，样品的特征在于与技术，如二次离子质谱杂质含量和X射线衍射晶体结构。武装的表征技术提供的基本信息，一个独特的模型被开发和EPR数据解释的电荷转移参数，如缺陷水平和热障。值得注意的是，因为时间依赖性光EPR探测特定缺陷，所以参数可以直接分配给该特定缺陷。因此，工作的最终结果是所识别的缺陷与该缺陷特有的电荷转移参数的关联。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical description: All of today's electronic gadgets, from cell phones to LEDs, are based on a class of materials called semiconductors. From single element materials like Si, which initiated the computer revolution, to multi-element materials like GaN, which ushered in the lighting revolution, semiconductors form the heart of electronic technology today. A subset of electronic materials known as oxide semiconductors have traditionally been used as gas sensors and optical windows. However, recent studies demonstrate the potential of oxides for electronic device applications as well. For instance, they can relatively easily be made into large sized crystals, a key factor for bulk device manufacturing. On the other hand, controlling the conductivity, which is essential for a successful electronic material, is not so easy. Therefore, the bulk of the research activities focus on investigating the source and mechanisms of the conductivity inherent to the potentially exciting family of oxide semiconductors. In part, the high conductivity of as-grown oxides crystals is determined by various types of defects. Better understanding of the nature, evolution and interaction of the defects in these materials, help determine the appropriate steps needed to control the defects and, therefore, the resulting conductivity. By participating in this research, undergraduate and graduate students benefit from long-time collaboration with experts in the field located at, for instance, the Naval Research Laboratory and various industrial manufacturing facilities.Technical description: The relationship between the conductivity of as-grown oxide semiconductors and the numerous defects plaguing the material is an ongoing debate. The research project aims to minimize the debate by investigating the oxides utilizing a technique which can simultaneously identify the defects and their effect on conductivity. Specifically, the work investigates the link between charge transfer among point defects and the inherent conductivity in a subset of oxide semiconductors most pertinent to electronic applications, i.e. tin oxide, indium oxide and gallium oxide. The method employed, time-dependent photo-induced electron paramagnetic resonance (photo-EPR), combines the power of magnetic resonance with time evolution of an optical response to monitor charge transfer among defects uniquely identified by EPR. The analysis of the time-dependent data depends on a model developed from knowledge of the various impurities in the material as well as the crystal structure. Therefore, samples are characterized with techniques such as secondary ion mass spectrometry for impurity content and x-ray diffraction for crystal structure. Armed with the basic information provided by the characterization techniques, a unique model is developed and the EPR data are interpreted in terms of charge transfer parameters such as defect levels and thermal barriers. Significantly, because time-dependent photo-EPR probes a specific defect, the parameters may be directly assigned to that specific defect. Thus, the ultimate outcome of the work is the association of an identified defect with charge transfer parameters unique to that defect. The knowledge obtained is then used to tune growth conditions for desired conductivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.