Graphene is a two-dimensional material with conical bands that touch at the Dirac or Charge-Neutrality point. Its zero bandgap and atomically thin body allow it to switch between n-type and p-type conduction when assembled into a field-effect transistor geometry. The current modulation however is limited due to a finite minimum conductivity at the Charge Neutrality point, which prevents us from using graphene for digital electronic applications.
We therefore investigate graphene as an optical and analog electronic material, where the low on-off ratio is less of a problem. Especially the high frequency (RF) electronic applications are promising since graphene can be gated efficiently and has high carrier mobility. The electron-hole symmetry in graphene leads to constant optical absorption over a large energy range and a sharp electrically-adjustable absorption edge due to Pauli blocking at twice the Fermi energy. I will show that the optical conductivity in the THz regime can also be influenced efficiently by electrostatic and chemical doping. Finally, we use photoconductivity microscopy to study contacts and pn junctions in graphene. High-speed graphene photodetectors are demonstrated.