Electronic Transport in Nanostructured and Amorphous Semiconductor Thin Films

非技术描述：由纳米晶体在薄膜非晶态基质中组成的复合材料可以表现出任何一个单独成分都不具有的新特性。这些复合结构结合了非晶态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。本项目的目标是研究自支撑纳米晶薄膜和非晶/纳米晶复合材料的电学性质，因为纳米晶的性质是系统变化的。为了阐明这种材料中异常导电性的机制，最近由原理调查员发现，在广泛的条件下合成了各种非晶态半导体和非晶态/纳米晶复合材料，测试了各种导电模型。一名研究生和本科生研究人员在这个项目上一起工作，学习各种材料合成和表征技术。这项研究与各种推广活动相结合，向广大受众宣传先进材料研究的重要性。技术描述：该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和纯非晶半导体中的电荷传输机制。样品是通过使用明尼苏达大学开发的先进的双室共沉积系统来制备的，该系统能够生长嵌入氢化非晶硅或锗的薄膜基质中的纳米硅或锗或绝缘氮化硅的各种复合材料。通过结构(透射式电子显微镜、傅里叶变换红外光谱和拉曼光谱)、光学(透射式和恒定光电流技术)和电学表征技术来评估材料的性能。利用对丝状导电过程高度敏感的1/f噪声光谱，以及热电势和霍尔效应测量，研究了纳米结构薄膜中的电荷输运，以探索最近报道的反常跳跃电导的机制。

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.