  A simple method for the creation of Ohmic contact to 2-D electron gas (2DEG)
in AlGaN/GaN high electron-mobility transistors (HEMTs) using Cr/Graphene layer
is demonstrated. A weak temperature dependence of this Ohmic contact observed
in the range 77 to 300 K precludes thermionic emission or trap-assisted hopping
as possible carrier-transport mechanisms. It is suggested that the Cr/Graphene
combination acts akin to a doped n-type semiconductor in contact with AlGaN/GaN
heterostructure, and promotes carrier transport along percolating Al-lean paths
through the AlGaN layer. This new use of graphene offers a simple and reliable
method for making Ohmic contacts to AlGaN/GaN heterostructures, circumventing
complex additional processing steps involving high temperatures. These results
could have important implications for the fabrication and manufacturing of
AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the
future.
