Tailoring the Functionality of ZnO via Highly Lattice Mismatched and Lattice Matched Alloying

非技术描述：氧化锌(ZnO)正在成为紫外线(UV)应用的首选材料之一，但仅在较窄的能量范围内。氧化锌之所以吸引人，是因为它在很宽的温度范围内是一种非常有效的发光材料，并且具有良好的化学性质。创造一种合金是一种定制光学性质并在所需能量下实现额外光发射的方法。因此，将氧化锌与某些原子成分合金化，可以为氧化锌增加新的光学和电学功能。合金的光学性能取决于它们的材料质量，以及氧化锌基质中的原子成分易于混合或溶解的程度。本项目的重点是研究两个氧化锌基合金体系，即Mg(X)Zn(1-x)O和ZnS(1-x)O(X)，目的是获得具有已知溶解度和材料性能的高质量合金，使其在设计上分别在高于和低于纯ZnO的能量范围内具有光学性能。特别是，合金可以提供在深紫外光和蓝绿光谱范围内具有可调带隙和新的光学发射的材料。这项研究对这些合金在蓝色和紫外光半导体光源和传感器等非常重要的领域的潜在用途，以及在恶劣环境下运行的敏感电子设备的保护涂层技术方面具有更广泛的影响。作为这项研究工作的一部分，还启动了一个教育推广计划，向当地社区提供一系列关于材料在消费技术中的作用的讲座。这项教育工作是与爱达荷大学哲学系的一位教授协调进行的，他的专长是加强跨学科研究中的交流和向公众转让科学技术知识。技术细节：在这项研究中，研究了促进立方相的高比例镁成分的Mg(X)Zn(1-x)O，目标是在4-6 eV的紫外区实现带隙工程合金，而研究ZnS(1-x)O(X)的目的是创造在可见光谱的蓝绿色部分具有带隙的材料。ZNS(1-x)O(X)是一种高度晶格失配的合金体系，可以用来实现新的电学和光学性质，如强烈的带隙弯曲到可见光谱，以及在掺杂样品的情况下将价带修改为受主能级分离。在这项研究中，合成了烧结陶瓷，以及通过溅射技术生长的薄膜。由于这两种生长技术的热平衡条件不同，对这两种材料的研究有望在合金的关键方面产生全面的知识，如溶解度极限、样品均匀度和亚稳。通过高分辨原子成像技术和X射线衍射仪研究了材料的性质，通过光致发光、拉曼散射、吸收和红外光谱研究了材料的光学性质。此外，还利用霍尔效应测量方法研究了掺杂的ZnS(1-x)O(X)的价-受主能级关系。实验研究与分析模型相辅相成。这项研究的结果使得在光谱的重要部分创造具有广泛带隙和新的发射线的材料成为可能。这项研究的另一个重要影响是，为了使氧化锌作为一种可行的材料在基于量子井的器件中发展，关于其合金系统的知识是必要的，因为合金构成了势垒成分。这项研究是爱达荷大学和附近华盛顿州立大学的两名个人投资机构共同努力的结果。一名博士后研究员、一名研究生和一名本科生得到了这项研究的支持和参与。由于私人投资机构致力于教育工作，其他几名来自不同背景的本科生也参与了这项研究。这两个实验室为学生和博士后研究人员提供了一个很好的机会，让他们获得光学材料的基础知识，并接受尖端研究技术的培训。

NON-TECHNICAL DESCRIPTION: Zinc oxide (ZnO) is emerging as one of the materials of choice for ultraviolet (UV) applications, but only at a narrow energy range. ZnO is attractive because it is a very efficient light-emitter in a wide range of temperatures, and has a benign chemical nature. Creating an alloy is one route for tailoring optical properties and achieving additional light emissions at desired energies. Thus alloying ZnO with certain atomic constituents can add new optical and electronic functionalities to ZnO. The optical properties of the alloys depend on their material quality, and on how amenable to mixing, or soluble, are the atomic constituents in the ZnO matrix. This project focuses on the study of two ZnO-based alloy systems, Mg(x)Zn(1-x)O and ZnS(1-x)O(x), with the objective of achieving high-quality alloys with known solubility and material properties that enable optical properties by design at energy ranges above and below that of pure ZnO, respectively. In particular, the alloys may provide materials with tunable bandgaps and new optical emissions in the deep-UV as well as in the blue-green spectral ranges. This research has broader impact in the potential use of these alloys in the highly vital field of blue and UV semiconductor light sources and sensors, as well as in coating technologies for the protection of sensitive electronic devices operating in harsh environments. As part of this research effort, an educational outreach program is also being initiated that presents a series of lectures to the local community on the role of materials in consumer technology. The educational effort is coordinated with a professor from the Department of Philosophy at the University of Idaho, whose expertise is in enhancing communication in cross-disciplinary research and on the transfer of scientific and technical knowledge to the general public.TECHNICAL DETAILS: In this research, Mg(x)Zn(1-x)O with a high percentage of Mg composition that promotes the cubic phase is investigated with the goal of achieving bandgap engineered alloys in the UV range of 4 - 6 eV, while ZnS(1-x)O(x) is studied with the objective of creating materials with bandgap in the blue-green part of the visible spectrum. ZnS(1-x)O(x) is a highly-lattice mismatched alloy system, and may prove useful for enabling new electronic and optical properties, such as strong bandgap bowing into the visible spectrum, and modification of valence band to acceptor level separation for the case of doped samples. For this research, sintered ceramics, as well as films that are grown via a sputtering technique, are synthesized. Due to the different thermal equilibrium conditions of these two growth techniques, studying both types of materials is expected to yield comprehensive knowledge into key aspects of the alloys such as solubility limits, sample homogeneities, and metastabilities. The material properties are studied via several high-resolution atomic imaging techniques and X-ray diffraction, while the optical properties are studied via photoluminescence, Raman scattering, absorption, and infrared spectroscopy. Additionally, Hall effect measurements are employed for the investigation of doped ZnS(1-x)O(x) for understanding the valence - acceptor levels relation. The experimental studies are complemented with analytical modeling. The outcome of this research enables the creation of materials with a broad range of bandgaps and new emission lines in an important part of the spectrum. Another significant impact of this research is that for the advancement of ZnO as a viable material in quantum-well based devices, knowledge concerning its alloy systems is necessary, as the alloy constitutes the barrier component. The research is a collaborative effort between two PIs from the University of Idaho and from nearby Washington State University. A postdoctoral researcher, one graduate student, and an undergraduate student are supported by and participate in this research. As the PIs are strongly committed to educational efforts, several other undergraduates from diverse backgrounds take part in the research. The two laboratories provide an excellent opportunity for the students and the postdoctoral researcher to gain basic knowledge in optical materials as well as be trained in cutting-edge research techniques.