  Self-heating is a severe problem for high-power GaN electronic and
optoelectronic devices. Various thermal management solutions, e.g. flip-chip
bonding or composite substrates have been attempted. However, temperature rise
still limits applications of the nitride-based technology. Here we demonstrate
that thermal management of GaN transistors can be substantially improved via
introduction of the alternative heat-escaping channels implemented with
few-layer graphene - an excellent heat conductor. We have transferred few-layer
graphene to AlGaN/GaN heterostructure field-effect transistors on SiC
substrates to form the "graphene-graphite quilts" - lateral heat spreaders,
which remove heat from the channel regions. Using the micro-Raman spectroscopy
for in-situ monitoring we have shown that temperature can be lowered by as much
as ~ 20oC in such devices operating at ~13-W/mm power density. The simulations
suggest that the efficiency of the "graphene quilts" can be made even higher in
GaN devices on thermally resistive sapphire substrates and in the designs with
the closely located heat sinks. Our results open a novel application niche for
few-layer graphene in high-power electronics.
