Contents 3.1 Introduction................................................................................................... 54

3.1.1 Metal Contacts to Conventional Semiconductors ...................... 54 3.1.2 Metal-Induced Gap States .............................................................. 55 3.1.3 Disorder-Induced Gap States ......................................................... 55 3.1.4 Bond Polarisation Model ................................................................ 56 3.1.5 Doping ............................................................................................... 56

3.2 General View of Metal Contact to Graphene ........................................... 57 3.3 Metal/Graphene Interactions ...................................................................... 58

3.3.1 Chemical Bonding of Metal with Graphene ................................ 59 3.3.1.1 Electrochemical Equalisation ........................................ 59 3.3.1.2 Orbital Hybridisation ..................................................... 60

3.4 Electrical Characterisation of Metal Contact to Graphene .................... 65 3.4.1 Current Flow Path at Metal/Graphene Interface ........................ 65 3.4.2 Transfer Length Method ................................................................ 66 3.4.3 Cross-Bridge Kelvin Method ......................................................... 68 3.4.4 Four-Probe Method and Graphene Resistivity

Underneath Metal ............................................................................ 69 3.4.5 Quantum Capacitance Measurements ......................................... 70

3.5 Process-Related Issues .................................................................................. 73 3.6 Eect of Contact Resistance on Graphene Devices ................................. 76

3.6.1 Metal-Insulation-Semiconductor Field-Eect Transistors ...... 76 3.6.2 RF Applications ................................................................................ 76

3.1 Introduction Since the pioneering research on graphene [1], many fundamental research studies have been carried out, and a number of new phenomena have been found ideal for the two-dimensional material. Electrical contacts, however, are critically important in addition to the surprisingly high electron and hole mobility from the viewpoint of the electron device applications of graphene. is is more signicant in the higher carrier mobility channel materials. It is noted that an interaction of metal/graphene might be dierent from those of conventional metals/semiconductors as there is no energy band gap in graphene. Nevertheless, it is worth considering similarities between them to understand what occurs at the metal/graphene interface. erefore, let us start with Schottky contacts on ordinary semiconductors.