Intrinsic and Extrinsic Donors and Acceptors in Zinc Oxide Crystals

氧化锌晶体中的内在和外在供体和受体

• 批准号: 0508140
• 负责人: Larry Halliburton
• 金额: --
• 依托单位: West Virginia University Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-06-15 至 2008-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0508140&HistoricalAwards=false
• 关键词: Intrinsic; Extrinsic; Donors; Acceptors; Zinc

TECHNICAL EXPLANATION This project addresses fundamental materials science issues associated with defects and impurities in zinc oxide (ZnO). The overall goal of the research is to obtain a complete understanding of the nature and behavior of donors and acceptors in ZnO, so that improvements in the growth and doping of ZnO crystals can be realized. Optical, electrical, and magnetic properties of bulk ZnO crystals will be studied using a variety of techniques including electron paramagnetic resonance, photoluminescence, optical absorption, and Hall effect. ZnO is a wide-band-gap semiconductor with excellent prospects to be a versatile and low-cost ultraviolet light emitter and detector. It is also a major participant in the emerging field of room-temperature spintronics. It has a large exciton binding energy of 60 meV and can easily be grown as large single crystals suitable for use as substrates in homoepitaxial film growth. However, before ZnO is able to reach its full potential, a better understanding of the shallow donors and acceptors must be developed. It is easy to produce n-type ZnO, but very difficult to produce p-type material. Significant progress in p-doping depends on minimizing the concentrations of unwanted donors and, at the same time, incorporating isolated acceptors that result in the desired electrical behavior. This is the motivation for investigation of donors that occur in ZnO without deliberate doping (e.g., native defects such as oxygen vacancies or zinc interstitials, or perhaps trace impurities in the starting materials). It is well known that the conductivity of ZnO is easily increased by annealing crystals in zinc vapor at temperatures near 1100C. The approach will be to determine whether the increase is caused by oxygen vacancies or zinc interstitials. A parallel set of experiments will explore the possibility that annealing ZnO in vacuum, nitrogen, or other reducing atmospheres increases the number of zinc interstitials in the material when a zinc-rich layer forms at the surface due to the removal of oxygen. In a second part of the project, large concentrations of oxygen vacancies and zinc vacancies will be produced by irradiation with high-energy electrons and protons. Electron paramagnetic resonance provides clear identification of such defects, and allows their associated absorption bands and luminescence features to be established. This information will then be used to monitor these defects in ZnO grown by different techniques and subjected to various anneal conditions. The third and fourth parts of the project address the electronic structure of acceptors such as nitrogen and lithium and the role of hydrogen in ZnO (i.e., to assess whether it is a shallow donor or simply a passivator of acceptors). The final two parts of the project address the properties of isolated transition-metal ions in ZnO (e.g., Mn2+, Co2+, V2+, Ni3+, Fe3+ and Cu2+) and the origin of an unstructured green luminescence band. Through this approach the project expects to identify the fundamental mechanisms that control the electrical conductivity of ZnO bulk crystals and thin films. NON-TECHNICAL EXPLANATIONThe project addresses fundamental materials research with strong technological relevance to electronics and photonics, and effectively integrates research and education. Project activities include campus visits and presentations at non-Ph.D. institutions in the region (Marshall University, Frostburg State University, West Virginia University Institute of Technology, West Virginia Wesleyan College, Fairmont State College, and Wheeling Jesuit University), the integration of ZnO-based research examples (including demonstrations) into the undergraduate solid-state physics course at West Virginia University, and the selection of an undergraduate physics or engineering major from an underrepresented group to work on the project (during the academic year and in the summer).

技术说明 该项目解决与氧化锌 (ZnO) 缺陷和杂质相关的基本材料科学问题。该研究的总体目标是全面了解 ZnO 中施主和受主的性质和行为，从而实现 ZnO 晶体生长和掺杂的改进。将使用电子顺磁共振、光致发光、光吸收和霍尔效应等多种技术来研究块状 ZnO 晶体的光学、电学和磁学特性。 ZnO是一种宽带隙半导体，具有成为多功能且低成本的紫外光发射器和探测器的良好前景。它也是新兴的室温自旋电子学领域的主要参与者。它具有 60 meV 的大激子结合能，可以轻松生长为大单晶，适合用作同质外延薄膜生长的衬底。然而，在 ZnO 能够充分发挥其潜力之前，必须更好地了解浅层供体和受体。制备n型ZnO很容易，但制备p型材料却非常困难。 p 掺杂的重大进展取决于最大限度地减少不需要的施主的浓度，同时合并隔离的受主，从而产生所需的电学行为。这是研究 ZnO 中没有故意掺杂（例如氧空位或锌间隙等天然缺陷，或者可能是起始材料中的微量杂质）的施主的动机。众所周知，通过在接近 1100℃ 的温度下在锌蒸气中对晶体进行退火，很容易提高 ZnO 的电导率。该方法将确定增加是由氧空位还是锌间隙引起的。一组平行的实验将探讨当由于氧的去除而在表面形成富锌层时，在真空、氮气或其他还原气氛中对 ZnO 进行退火会增加材料中锌间隙原子数量的可能性。在该项目的第二部分中，将通过高能电子和质子的辐照产生高浓度的氧空位和锌空位。电子顺磁共振可以清楚地识别此类缺陷，并允许建立其相关的吸收带和发光特征。然后，该信息将用于监测通过不同技术生长并经受各种退火条件的 ZnO 中的这些缺陷。该项目的第三和第四部分讨论了氮和锂等受体的电子结构以及氢在 ZnO 中的作用（即评估它是浅供体还是简单的受体钝化剂）。该项目的最后两部分解决了 ZnO 中孤立过渡金属离子（例如 Mn2+、Co2+、V2+、Ni3+、Fe3+ 和 Cu2+）的特性以及非结构化绿色发光带的起源。通过这种方法，该项目期望确定控制 ZnO 块状晶体和薄膜电导率的基本机制。非技术说明该项目致力于与电子和光子学具有很强技术相关性的基础材料研究，并有效地将研究和教育结合起来。项目活动包括校园参观和非博士学位演讲。该地区的机构（马歇尔大学、弗罗斯特堡州立大学、西弗吉尼亚大学理工学院、西弗吉尼亚卫斯理学院、费尔蒙特州立学院和惠灵耶稣会大学），将氧化锌基研究实例（包括演示）整合到西弗吉尼亚大学的本科固体物理课程中，并从代表性不足的群体中选择物理或工程专业的本科生来从事该项目（在学术期间） 年和夏季）。