Silicon semiconductors reach their limits at more than ten gigahertz, and even compound semiconductors such as silicon germanium( SiGe) have their cutoff frequencies at around 60 GHz. But how do you deal with higher frequencies, with millimeter waves up to 300 GHz or with sub-millimeter waves?
New carbon compounds called graphene have been invented for these frequency ranges. These have a two-dimensional carbon structure in which each carbon atom is connected to three other carbon atoms. This results in a honeycomb-like arrangement of the atoms.
IBM researchers have developed diodes, transistors, graphene ICs and memory chips from graphene. For this purpose, individual layers and electrodes were applied and structured in a complicated, multi-step process. With the chemical vapor deposition used in this process, the graphene is deposited.
Since graphene is electrically conductive and can also absorb light in a wide wavelength range, it is also used in image sensors. The light sensitivity is extremely high, since each incident photon emits a multiple of electrons. With the GQD sensor, there is an image sensor that is much more light-sensitive than conventional image sensors.