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

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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.