Electronic Properties of Amorphous Semiconductors

本项目主要研究非晶半导体中缺陷的基本性质。首先，研究将进一步验证和理解氢化非晶硅（a-Si:H）中新型的深度缺陷弛豫，这是在本研究的前一阶段通过电容瞬态测量提出的。这些实验研究将集中在(1)通过其对与a- si:H中深度缺陷相关的光谱的影响来观察弛豫，以及(2)将调制光电流光谱（也表明缺陷弛豫效应）与电子自旋共振数据进行比较，以确定负责的深度缺陷子带。其次，该项目将研究含有四面体键（ta-C）优势的新型碳的深度缺陷特性。这种材料最近被制成具有足够好的半导体特性，可以适用于我们的结电容方法。所披露的深度缺陷性质可能与基于Si和Ge的四面体非晶半导体具有根本不同。非晶或“玻璃”材料代表了一个真正的前沿领域，以测试我们对固态物理的理解。这类材料中越来越重要的一类是非晶半导体，如氢化非晶硅（a-Si:H）。后一种材料在光电和用于驱动液晶显示器（平板电视）的薄膜晶体管阵列中得到了重要的技术应用。然而，对a-Si:H的理论认识还处于起步阶段。本实验研究旨在了解这类材料中缺陷的基本电子特性。这些缺陷目前限制了它们未来的技术开发。特别令人感兴趣的是在a- si:H中新发现的缺陷行为方面，这表明电子结构本身具有玻璃化的方面。此外，还将对一种新型非晶半导体——四面体非晶碳（晶体金刚石的非晶对应物）的电子特性进行初步研究。＊＊＊

w:\awards\awards96\*.doc 9624002 Cohen This project involves research into the fundamental properties of defects in amorphous semiconductors. First, studies will be carried out to further verify and understand the novel type of deep defect relaxation in hydrogenated amorphous silicon (a-Si:H) that has been suggested by capacitance transient measurements in the previous phase of this research. These experimental studies will focus on (1) observing relaxation through its effect on the optical spectra associated with deep defects in a-Si:H, and (2) comparing modulated photocurrent spectra (which also indicate a defect relaxation effect) with electron spin resonance data to identify the deep defect sub-bands responsible. Second, the project will investigate the deep defect properties of a novel form of carbon containing a predominance of tetrahedral bonding (ta-C). This material has recently been made with sufficiently good semiconducting properties to be amenable to our junction capacitance methods. The disclosed deep defect properties are likely to be fundamentally different than those of the tetrahedral amorphous semiconductors based on Si and Ge. %%% Amorphous or "glassy" materials represent a true frontier area to test our understanding of solid state physics. One increasingly important class of such materials are amorphous semiconductors such as hydrogenated amorphous silicon (a-Si:H). This latter material is finding important technological applications in photovoltaics and in thin film transistor arrays used to drive liquid crystal displays (flat panel TV). However, the theoretical understanding of a-Si:H is still in its infancy. This experimental research is directed at understanding the basic electronic properties of defects in such materials. These defects currently limit their future technological exploitation. Of partic ular interest are newly discovered aspects of the defect behavior in a-Si:H which suggests a glassy aspect to the electronic structure itself. In addition, preliminary studies of the electronic properties of a relatively new type of amorphous semiconductor, tetrahedral amorphous carbon (the amorphous counterpart of crystalline diamond) will be initiated. ***