Study of Light Induced Effects on the Carrier Transport Property in Amorphous Silicon

无序固体的频率相关电导率一直是人们感兴趣的课题，并从各种导电系统的微观和宏观图像中进行了论证。最近的实验研究表明，存在着“通用”的频率标度的归一化交流电导率，这是发现，以及在理论上再现的极其无序的系统，其中跳跃电荷传导通过强烈的本地化/绑定网站是占主导地位的。在这些讨论中排除的是在非晶半导体中的迁移率边缘附近的交流电子电导率，这可能表现出类似的标度特征。这项工作的目的是，然后，追求通用的交流缩放的迁移率边缘的电子电导率，以及推断的信息要从测量中提取，特别是光诱导效应的带边载流子输运。基于弱局域化问题的重整化群处理方法，研究了迁移率边附近的频率和温度依赖的电子传导。由其直流对应归一化的交流电导率被发现遵循一个简单的普适性方程是非常相似的服从共同为各种不同的跳跃传导系统。将理论结果应用于氢化非晶硅在退火态和光浸泡态交流电导的实验数据，结果表明光浸泡并不改变导带边局域态的能量宽度，导带边局域态的能量宽度保持在100 meV左右。

The frequency dependent (ac) conductivity being characteristic to disordered solids has been long a subject of great interest, and argued from both the microscopic and macroscopic pictures of various conduction systems. Recent experimental studies have revealed an existence of "universal" frequency-scaling of the normalized ac conductivity, that is found to be well reproduced theoretically for extremely disordered system in which hopping charge conduction via strongly localized/bound sites is predominant. What is excluded in these discussions is the ac electronic conductivity near the mobility edge in amorphous semiconductors which is likely to exhibit similar scaling feature. The aim of this work is, then, to pursue the universal ac scaling for the mobility edge electronic conductivity as well as to infer to the information to be extracted from the measurements, especially the light induced effects on the band-edge carrier transport. Frequency and temperature dependent electronic conduction near the mobility edge is investigated on the basis of the renormalization group treatment for weak localization problems. The ac conductivity normalized by its dc counterpart is found to follow a simple universality equation being quite similar to that obeyed in common for various different hopping conduction systems. The theoretical results have been applied to the experimental data sets acquired on the ac conductivity of hydrogenated amorphous silicon in the well-annealed and light-soaked states, indicating that the the energy width of the conduction band edge localized states is not changed by light-soaing, and stays at aroud 100 meV.