High-K dielectric depositions (aluminum oxide) using ozone-based ALD (atomic layer deposition) for graphene-based devices

The aim of this dissertation is to develop ALD gate dielectric process (O3-based ALD dielectric) for graphene-based devices, study an ALD process reaction with graphene and growth mechanism, and demonstrate the electrical performance of the graphene devices. This ALD dielectric for graphene-based devices should provide minimal chemical doping and no process-induced defects into graphene, and exhibit good dielectric properties as well as high carrier mobility in top-gated graphene devices.In this study, effects of ALD oxidants on the growth behavior of Al 2O3 films on highly oriented pyrolytic graphite (HOPG) substrate are discussed. H2O-based ALD process reveals that the Al2 O3 film is selectively deposited along step edges while O 3-based ALD process provides conformal deposition on HOPG, potentially by forming epoxide group. The Al2O3 layer deposited using the O3 process on HOPG does not introduce a significant defect concentration to the top graphene layer and good dielectric properties such as dielectric constant &sim9 and a reasonable leakage current of 3.4x10 -8A/cm2 at -1V.Ozone adsorption on graphene is studied using the ab initio density functional theory method. It shows physisorption and chemisorption states of ozone molecules adsorbed on graphene and the effective energy barrier for chemisorption state (epoxide), and shows the binding energy to be 0.25eV for physisorption and 0.33eV for chemisorption, respectively. The effects of ozone process on graphene layer are discussed using Raman spectroscopy and exhibits thickness-dependent behavior, implying the enhanced reactivity of single-layer graphene deposited on SiO2 by influence of the substrate.The effects of ozone adsorption on the carrier transport of graphene devices are studied by the density of states calculation and in-situ electrical measurements. This study reveals that O3 adsorption on graphene at 25°C is likely governed by physisorption. Also, ALD Al 2O3 layer deposition using O3 on single-layer graphene is investigated using Raman and electrical measurements. A correlation between Raman spectrum and resultant electrical results is observed for single-layer graphene devices, indicating that the Al2O3 deposition at 25°C can be used for functionalization layer. Top-gate graphene devices with O3-based Al2O3 dielectric show a heterojunction structure as well as a high mobility of 3000&sim5000cm2/Vs at 25°C in ambient condition.