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

非技术描述：今天所有的电子设备，从手机到LED，都是基于一种被称为半导体的材料。从开启计算机革命的硅这样的单元素材料，到引领照明革命的GaN这样的多元素材料，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一个子集传统上被用作气体传感器和光学窗口。然而，最近的研究也证明了氧化物在电子设备应用中的潜力。例如，它们可以相对容易地制成大尺寸晶体，这是制造大宗设备的关键因素。另一方面，控制电导率并不那么容易，这是成功的电子材料所必需的。因此，大部分研究活动集中在调查潜在的激动人心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，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、演化和相互作用，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电导率。通过参与这项研究，本科生和研究生受益于与该领域专家的长期合作，例如，海军研究实验室和各种工业制造设施。技术描述：生长的氧化物半导体的导电性与困扰材料的许多缺陷之间的关系是一个正在进行的辩论。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调查氧化物，从而将争论降至最低。具体地说，这项工作研究了点缺陷之间的电荷转移与与电子应用最相关的一组氧化物半导体的固有导电性之间的联系，即锡氧化物、氧化铟和氧化镓。该方法采用依赖于时间的光致电子顺磁共振(Photo-EPR)，将磁共振的能量与光学响应的时间演化相结合，以监测由EPR唯一识别的缺陷之间的电荷转移。对随时间变化的数据的分析依赖于根据材料中的各种杂质以及晶体结构的知识建立的模型。因此，样品用二次离子质谱分析杂质含量和X射线衍射分析晶体结构等技术进行表征。利用表征技术提供的基本信息，建立了一个独特的模型，并根据缺陷能级和热垒等电荷转移参数解释了EPR数据。值得注意的是，由于依赖时间的光电子顺磁共振探测特定的缺陷，因此参数可以直接分配给该特定的缺陷。因此，这项工作的最终结果是确定的缺陷与该缺陷特有的电荷转移参数之间的关联。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.