Electronic Transport in Nanostructured and Amorphous Semiconductor Thin Films

非技术描述：由薄膜无定形基质中的纳米晶体组成的复合材料可以表现出不具有任何单个成分特征的新特性。这些复合结构结合了非晶半导体的优点和纳米晶体的独特性质，可能会使新的电子和光伏应用成为可能。本计画的目的是研究自支撑奈米薄膜及非晶/奈米复合材料的电子性质，因为奈米薄膜的电子性质会有系统的变化。为了阐明这种材料中不寻常的导电性的机制，最近发现的主要研究者，各种非晶半导体和非晶/纳米晶复合材料，在广泛的条件下合成的研究，测试各种导电模型。一名研究生和本科生研究人员在这个项目上合作，学习各种材料合成和表征技术。该研究与各种外展活动相结合，向广大受众宣传先进材料研究的重要性。技术说明：研究项目的目标是阐明独立纳米晶薄膜、含有纳米晶夹杂物的非晶半导体复合材料以及纯非晶半导体中的电荷传输机制。通过采用明尼苏达大学开发的先进的双室共沉积系统制造样品，该系统能够生长嵌入氢化非晶硅或锗或绝缘氮化硅的薄膜基质中的非晶硅或锗的各种复合材料。通过使用结构（透射电子显微镜，傅里叶变换红外光谱，和拉曼光谱），光学（传输和恒定光电流技术）和电学表征技术的材料性能进行评估。纳米结构薄膜中的电荷输运的研究，通过使用1/f噪声光谱，是非常敏感的导电过程，以及热功率和霍尔效应测量，以探索机制的基础上最近报道的异常跳跃电导率。

Non-Technical Description: Composite materials consisting of nanocrystals within a thin-film amorphous matrix can exhibit novel properties not characteristic of either individual constituent. These composite structures, combining the advantages of amorphous semiconductors with the unique properties of nanocrystals may enable new electronic and photovoltaic applications. The goal of this project is to study the electronic properties of free-standing nanocrystalline films and amorphous/nanocrystalline composites as the nanocrystal properties are systematically varied. In order to elucidate the mechanism underlying the unusual conductivity in this type of material, recently discovered by the Principle Investigator, a variety of amorphous semiconductors and amorphous/nanocrystalline composites, synthesized under a broad range of conditions are investigated, testing various conduction models. A graduate student and undergraduate researchers work together on this project, learning a variety of materials synthesis and characterization techniques. The research is integrated with various outreach activities, promoting the importance of advanced materials research to a wide audience.Technical Description: The goal of the research project is to elucidate the charge transport mechanisms in free-standing nanocrystalline films; composite materials of amorphous semiconductors containing nanocrystalline inclusions; and pure amorphous semiconductors. Samples are fabricated by employing an advanced dual-chamber co-deposition system, developed at the University of Minnesota, that enables growth of various composite materials of a nanocrystal Si or Ge embedded in a thin-film matrix of hydrogenated amorphous silicon or germanium, or an insulating silicon nitride. The material properties are evaluated by using structural (transmission electron microscopy, Fourier transform infra-red spectroscopy, and Raman spectroscopy), optical (transmission and constant photocurrent techniques) and electrical characterization techniques. The charge transport in nanostructured films is investigated by using 1/f noise spectroscopy that is highly sensitive to filamentary conduction processes, as well as thermopower and Hall-effect measurements, in order to explore the mechanisms underlying the recently reported anomalous hopping conductivity.