GaN baed HEMTs are very promising transistors for high power and high efficiency amplifiers due to the very high power density of 10 W/mm. However, the high power density put high demands on the thermal conductivity of the semiconductor substrate. The intrinsic temperature of the HEMT will increase significantly if the generated heat due to the dissipated power is not transported away. The GaN HEMT is fabricated on top of a SiC substrate, and the SiC is a very good thermal conductor. But an AlN nucleation layer is needed to “glue” the SiC substrate and the GaN buffer together. The nucleation layer significantly reduces the thermal conductivity. It is therefore important to characterize the thermal conductivity for different layers to understand how to improve the overall thermal conductivity for GaN based HEMTs.
 
The work consists of a literature study, to understand device fabrication and electro-thermal characterization. Thereafter, the student will fabricate test structures on materials with different nucleation layers in our clean room. These test structures will then be measured on in our measurement lab.
This thesis is carried out within the GigaHerz centre and the student will therefore present the results on meetings together with our industrial partners. This gives to student good opportunities to meet engineers and researchers from world leading companies within the microwave industry.
Contact person: Dr. Mattias Thorsell (mattias.thorsell@chalmers.se) , tel. 031 - 772 1896