The impact of width-induced inhomogeneity on the carrier transport in graphene system

• Main Authors: Wei-Yuan Yang, 楊維元
• Other Authors: 梁啟德
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/08827510898616087589

碩士 === 國立臺灣大學 === 物理學研究所 === 104 === Ever since graphene, a single layer of graphite, was realized experimentally by the mechanically exfoliated method in 2004, it has become a major field of interest in the condensed matter physics. It has many fascinating properties, such as high electric conductivity, thermal conductivity, and mobility, etc. Also, with the features of massless fermion as carriers, many researches have been focused on the investigation in high-mobility graphene devices. On the other hand, low-mobility ones also show great potential with an opened band gap and other impurities-scattering effects. In this thesis, we focus on the width effect in a disordered graphene system to its electronic transport properties. By using processes involving a photolithography method, we patterned our chemical vapor deposited (CVD) graphene into devices with different channel width Hall bars. The channel widths of our devices are 1.25, 5.90, and 25.09 μm respectively. Current-voltage (I-V ) measurements were performed from 2 K to 30 K with a 2 K temperature increment. At the low temperature region, the nonlinear I-V curve at the low field region was observed. The resistance-temperature (R-T ) diagrams, which reveals the hopping mechanism within each channel, was derived through differentiating the inversed slope of the I-V diagrams. By comparing the R-T diagrams among three devices, the one with narrowest channel width was found to have the highest current density. Combing these results with the standard deviation of impurity strengths acquired from Raman spectroscopy, we conclude that the width induced inhomogeneity in a graphene system can act as a major impact on its electronic transport behavior. Our work opens the door to the study of graphene samples with different channel widths. More works could be investigated in the near future, including subjects regarding high-mobility samples and the transport under a vertical magnetic field. Other intrinsic effects may come out to complete the whole picture on the transport behavior of this fascinating material.