Electronic Transport in Nanostructured and Amorphous Semiconductor Thin Films

非技术描述：由薄膜非晶基质内的纳米晶体组成的复合材料可以表现出任何一种单独成分所没有的新颖特性。这些复合结构将非晶半导体的优点与纳米晶体的独特性能相结合，可以实现新的电子和光伏应用。该项目的目标是研究独立式纳米晶薄膜和非晶/纳米晶复合材料的电子特性，因为纳米晶体特性是系统变化的。为了阐明这种材料中异常导电性的机制，原理研究员最近发现了这种材料，研究了在各种条件下合成的各种非晶半导体和非晶/纳米晶复合材料，测试了各种导电模型。研究生和本科生研究人员共同参与该项目，学习各种材料合成和表征技术。该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自支撑纳米晶薄膜中的电荷传输机制；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。样品是通过采用明尼苏达大学开发的先进双室共沉积系统制造的，该系统能够生长嵌入氢化非晶硅或锗或绝缘氮化硅薄膜基质中的纳米晶体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（透射和恒定光电流技术）和电表征技术来评估材料特性。通过使用对丝状传导过程高度敏感的 1/f 噪声光谱以及热电势和霍尔效应测量来研究纳米结构薄膜中的电荷传输，以探索最近报道的异常跳跃电导率的机制。

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.