Heteroepitaxy of Near-Single Crystal Semiconductors on Flexible Cube-Textured Ni Sheet

非技术描述：迄今为止，在单晶衬底上生长的单晶半导体薄膜用于高性能半导体器件。然而，单晶衬底对于太阳能电池和显示器等大面积应用来说是昂贵的。多晶或非晶半导体薄膜成本低，但效率差。在这个项目中，近单晶薄膜的创造为在柔性金属薄片上制造各种半导体提供了一个新的范例，这些半导体具有优越的光电性能，可以以低成本和减少材料利用率的方式广泛应用于太阳能电池和显示技术中。此外，对不同薄膜织构、畴和缺陷形成机制的基本理解可以对燃料电池电极织构形成、各向异性磁记录和高温超导材料等许多研究领域产生广泛影响。该项目集研究、教育和外展活动于一体。在培养博士生的同时，创建适合本科生参与的研究项目。研究团队还积极开展外展活动，包括参与纽约州新愿景STEM（科学技术工程和数学）计划，为首都地区高中高年级学生提供服务。这些努力将提高学生追求科学和工程事业的兴趣。技术描述：研究小组研究了近单晶半导体薄膜（如Ge）在柔性立方体织构Ni（100）片上的外延生长。这些薄片是低成本的材料，具有非常大的颗粒，尺寸从50到100微米不等，所有的颗粒都具有大致相同的面内和面外方向。由于半导体-金属界面的合金化反应，大多数半导体不能在金属（如Ni）上外延生长。在本项目中，通过在Ni（100）片上沉积CaF2（111）外延层作为缓冲层和扩散屏障来防止合金化反应。然后在缓冲的Ni（100）衬底上外延生长近单晶Ge（111）。该项目的一个关键目标是减少/消除由于薄膜和衬底之间不对称而可能在生长过程中出现的Ge（111）旋转畴，以及当它们发生时域边界的钝化。利用原子学方法，包括量子力学密度泛函理论，进行计算建模，以帮助实验优化生长参数，并了解畴边界的结构和电子性质及其钝化。我们的最终目标是生产接近单晶的锗薄膜，作为可扩展的衬底，以生长功能半导体，如CdTe， GaAs或Si，其光电质量与单晶一样好或接近。

Non-technical Description: To date, single-crystal semiconductor films grown on single-crystal substrates are used in high-performance semiconductor devices. However, single-crystal substrates are expensive for large-area applications such as solar cells and display. Polycrystalline or amorphous semiconductor films can be low cost, but the efficiency is poor. The creation of near-single-crystal thin films in this project points to a new paradigm on the fabrication of a wide range of semiconductors on flexible metal sheets with superior optoelectronic properties that can be widely implemented in solar cell and display technologies at a low cost and with a reduction in material utilization. In addition, fundamental understanding of the mechanisms of different thin-film texture, domain and defect formations can impact broadly on many areas of research such as texture formation of electrodes in fuel cells, anisotropic magnetic recording, and high-temperature superconducting materials. The project integrates research, education, and outreach activities. In addition to training PhD students, research projects suitable for undergraduate students to participate are created. The research team also has active outreach activities including the participation of New York State New Visions STEM (Science Technology Engineering and Math) program for capital district high-school seniors. These efforts will enhance students' interest in pursuing science and engineering careers.Technical Description: The research team studies the epitaxial growth of near-single-crystal semiconductor films such as Ge on flexible, cube-textured Ni(100) sheets. These sheets are low-cost materials having very large grains ranging from 50 to 100 micrometers in size with all the grains having approximately the same in-plane and out-of-plane orientations. Most semiconductors do not grow epitaxially on metals such as Ni due to the alloying reaction at the semiconductor-metal interface. In this project, this alloying reaction is prevented by depositing an epitaxial layer of CaF2(111) on the Ni(100) sheet as a buffer layer and as a diffusion barrier. Near-single-crystal Ge(111) is then epitaxially grown on the buffered Ni(100) substrate. A key goal of the project is the reduction/elimination of the Ge(111) rotational domains that may occur during the growth due to dissimilar symmetry between the film and the substrate and also the passivation of the domain boundaries when they occur. Computational modeling using atomistic methods, including quantum-mechanical density functional theory, are employed to assist the experimental optimization of the growth parameters and to understand the structural and electronic properties of domain boundaries and their passivation. Our ultimate goal is to produce near-single-crystal Ge films as scalable substrates to grow functional semiconductors such as CdTe, GaAs, or Si with optoelectronic qualities as good as or close to that of single crystals.