Studies on Quantum Transport Mechanism of Si Quasi-One-Dimensional Carrier Systems by a Time-of-Flight Method with Pulse Lasers

本工作的目的是在硅中实现低维载流子体系，并明确该体系中的输运机制。我们研究了一维系统的制备条件与观测到的载流子输运机制之间的关系。用飞行时间法研究了Si_<1-x>Ge_x/Si体系中载流子的寿命。Si_<1-x>Ge_x/Si薄膜有望成为在硅上实现低维体系的材料。采用FIB法在n-Si上制备了p-Si导电丝。在2K ~ 300K的温度范围内测量了电流-电压特性。可以观察到三种特征输运；金属传导，最近邻跳频传导，一维可变跳频传导。观察到的输运机理与制备条件之间存在着系统的关系。实验结果表明，通过改变退火温度和杂质剂量，可以控制金属丝中的m含量。通过测量横向磁电阻，研究了跳变传导中的局域态信息。在低杂质浓度的样品上观察到负磁阻，对于最近邻跳变导大于15K的样品，表明存在安德森局域化。另一方面，在强磁场中，所有样品都出现正磁阻。对正磁电阻的分析表明，局域化是由于库仑势的限制。这些事实意味着两种局域态的存在。利用脉冲激光的飞行时间法研究了纳米级半导体器件中的输运现象。本实验选择未掺杂的Si_<1-x>Ge_x薄膜作为测试材料。得到了载体寿命与缺陷数量之间的关系。综上所述，该方法可用于评估寿命和局域态密度。少

The purpose of this work is to realize the low-dimensional carrier system in silicon and to make clear the transport mechanism in this system. We have examined the relationship between the fabrication condition of one-dimensional systems and the observed carrier transport mechanism. The life time of carriers in Si_<1-x>Ge_x/Si systems has been studied by means of the Time-of-Flight method. Si_<1-x>Ge_x/Si films are expected as a material for realizing low-dimensional systems on silicon.Electrical conductive wires of p-Si were fabricated on n-Si by FIB.The current-voltage characteristic was measured in the temperature range of 2K to 300K.Three kinds of characteristic transport can be observed ; the metallic conduction, the nearest neighbor hopping conduction, and the one dimensional variable hopping conduction. There exists a systematic relationship between the observed transport mechanism and the fabrication condition. In the experiments, it can be concluded that the transport mechanis … More m in the wire are controlled by changing the annealing temperature and the impurity dose.The information of localized states in the hopping conduction were studied with the measurements of transverse magnetoresistance. The negative magnetoresistance is observed on the sample with low impurity concentrations, for the sample with the nearest neighbor hopping conduction above 15K, which suggests the existence of Anderson localization. On the other hand, in the strong magnetic field, the positive magnetoresistance appears for all samples. The analysis of the positive magnetoresistance indicates that the localization is due to the confinement by the Coulomb potential. These facts mean the existance of two kinds of localized states.The Time of Flight method with pulse lasers was used for the study of transport phenomena in nano-scale semiconductor devices. In this experiments, undoped Si_<1-x>Ge_x thinfilms were selected as a test material. We have obtained the relationship between the carrieer life time and the amount of the defects. In conclusion, the method is useful for evaluating the life time and the localized state density. Less