Localized Electronic States in Amorphous Semiconductors

这项研究是对无序半导体的电子和结构性质的现有项目的延续和重新定向。一个主要的重点是光暗化效应，这是在大于光学带隙的能量的能量下的光学激发之后，光学吸收边缘向较低能量的亚稳态移位。这个项目的主要目标是开发一个详细的微观描述的变化，发生在砷和硫属元素的网站上的光暗化。第二个推力涉及光激发的电子和空穴在非晶半导体中的衰减，这种衰减发生在低温和光激发停止后很长一段时间。这些问题将通过熔体淬火、溅射和PECVD生长技术、磁共振光谱（ESR、NMR和NQR）光谱、光学和磁共振技术的各种组合、应用于特定硫族化物玻璃系统的电学和声学测量来解决。本工作的具体任务是：发展对硫系玻璃中光暗化前后局部结构有序细节的理解;确定硫系原子对光激发电子和空穴衰减的影响，这在四面体配位的非晶半导体中似乎是普遍的;在纳米尺度上检查部分结晶和各向异性的硫系玻璃;用声速和衰减法研究了玻璃的刚性逾渗阈值;研究了硫系玻璃从低平均配位数到高平均配位数结构变化过程中的本征缺陷;研究了分子氢在IV族硫系玻璃中的作用及其与玻璃可结晶性的可能关系。 这项工作将与学生和博士后研究助理进行。%非晶、微晶和纳米晶半导体目前用于或预期用于许多应用中，包括平板显示器、红外光纤和检测器以及太阳能电池。 尽管有这些成功的应用，但很少有普遍的性质来提供对这些材料的一般理论理解。 这项研究的重点是调查某些类型的玻璃的电和光激发如何在很长一段时间内衰减。这些研究的目标是发展对这些和相关过程的原子/分子水平的理解。 这项研究将与学生和博士后研究人员一起进行，他们将为在工业，政府和企业就业做好准备。

This research is a continuation and redirection of an existing project on the electronic and structural properties of disordered semiconductors. One major emphasis is the photodarkening effect, which is a metastable shift of the optical absorption edge to lower energies after optical excitation at energies greater than the energy of the optical band gap. The primary goal of this project is to develop a detailed microscopic description of the changes that occur at arsenic and chalcogen sites on photodarkening. A second thrust concerns the decay of optically excited electrons and holes in amorphous semiconductors that occurs at low temperatures and at long times after cessation of the optical excitation. These problems will be attacked by means of melt quenching, sputtering and PECVD growth techniques, magnetic resonance spectroscopy (ESR, NMR, and NQR) optical spectroscopies, various combinations of optical and magnetic resonance techniques, electrical and acoustic measurements applied to specifically selected chalcogenide glass systems. The specific tasks of this work are: to develop an understanding of the details of the local structural order before and after photodarkening in chalcogenide glasses; to ascertain the influence of chalcogen atoms on the decay of photo-excited electrons and holes that appears to be universal in the tetrahedrally-coordinated amorphous semiconductors; to examine partially crystallized and anisotropic chalcogenide glasses on a nanometer scale; to investigate the rigidity percolation threshold using sound velocity and attenuation methods; to study the intrinsic defects in chalcogenide glasses as the structure goes from low average to high average coordination number; and to study the role played by molecular hydrogen and the possible relationship with metastabilities in group IV-chalcogenide glasses. This work will be performed with students and postdoctoral research associates.%%%Amorphous, microcrystalline and nanocrystalline semiconductors are currently used, or are contemplated for use, in many applications, including flatpanel displays, infrared optical fibers and detectors, and solar cells. In spite of these successful applications there are very few universal properties to provide a general theoretical understanding of these materials. This research is focused on the investigation of how electrical and optical excitations of certain types of glasses decay over a long period of time. The goal of these studies is the development of an atomic/molecular level of understanding of these and related processes. This research will be performed with students and postdoctoral research associates who will thereby be prepared for employment in industry, government and academe.***