MICROSCOPY OF FUNCTIONAL INTERFACES IN GaN DEVICES
B. Pécz
Research Centre for Natural Sciences, Institute for Technical Physics and Materials Science,
Hungarian Academy of Sciences (MTA TTK MFA)
1121 Budapest, Konkoly-Thege u. 29-33, Hungary
Corresponding author: pecz.bela@ttk.mta.hu
Self-heating of high power devices is a major problem in GaN high electron mobility
transistors (HEMT), in which the power reached the values of 10 W/mm (the length of the gate
in mm). Therefore the heat dissipation became one of the major issues and substrates with high
heat conductivity are needed. Apparently there are two kinds of materials with excellent thermal
conductivity which can be used: diamond and graphene.
Two examples using diamond are shown. In the first one GaN layers (device structures)
were grown on diamond substrates by molecular beam epitaxy and the deposition process was
optimised using transmission electron microscopy (TEM). The grown GaN layers are free of
inversion domains and are of high quality.
The second example is a polycrystalline diamond coating layer which covers the grown
HEMT transistor and provides a heat sink for the high power devices close to the active region.
The third example shows how one can grow GaN over a graphene/SiC substrate. TEM
investigations are used to determine the dislocation density in grown GaN and to explore the
nanoscale details of the grown structure.