טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentHajaj Eitan M.
SubjectElectrical Properties of Single Layar Graphene
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor Dr. Yuval Yaish
Full Thesis textFull thesis text - English Version


Abstract

Since its first successful isolation, single layer graphene (SLG) has been the subject of many experimental and theoretical studies. Several experiments were conducted on SLG and, indeed, found the predicted non-interacting DOS, with a small correction to the graphene’s inverse compressibility due to electron-electron interaction. In most of these studies, the basic technique is based on measuring the change in the graphene’s chemical potential, under gate voltage periodic modulation, which is responsible for the change in the charge carrier density.

Recent experimental results suggest that, due to inhomogeneous surface potential, as the system is tuned towards the Dirac point, the graphene layer breaks into puddles in which electrons and holes coexist. A common method to extract the densities of electrons and holes is based on the two band model for the Hall Effect. However, this method is inadequate for the inhomogeneous regime, where, even though electrons and holes coexist, they do not share the same region in space. This obstacle may lead to inaccurate estimation of the electron-electron exchange and correlation contributions, which are of significant physical importance due to their many-body origin.

In this work we suggest a new method for directly measuring the chemical potential of SLG as function of carrier densities and temperatures, and derive from it the inverse compressibility and the DOS. Usually, the geometric capacitance is much smaller than the quantum capacitance, and the chemical potential gives only a small contribution to the electrostatic analysis, which makes measurements of the DOS challenging. We prepare graphene field effect devices comprised of mechanically exfoliated SLG on top of highly p-doped silicon substrates with a thin dielectric layer, resulting in high gate geometrical capacitance, charge carriers mobility, and the highest trans-conductance reported so far.

Analysis self-consistently the chemical potential and transport data, using the disorder strength parameter (DSP) as a single fitting parameter, we can extract the DSP, the charge carriers’ densities, the chemical potential, and the inverse compressibility. In addition, from our analysis we extract the temperature dependence of the charge carriers’ densities, sheet resistance, and DSP. We found a non-monotonous temperature behavior of the sheet resistance, which is mainly attributed to changes in the charge carriers’ densities due to the surface potential DSP temperature dependence. By extracting the electron and hole densities one can delineate their temperature dependence from the overall sheet resistance temperature dependence, and accurately study the different scattering mechanisms that govern graphene resistivity.