DC characterization of GaN-based microstrip HEMT for fabrication steps

GaN based microstrip high electron mobility transistors (HEMTs) have superior properties such as high-power density, high efficiency and high breakdown voltage. Thanks to these features, GaN-based HEMTs are more preferred in radar and space research systems and defense industry applications. In this thesis, direct current (DC) measurements were performed for the fabrication steps of 2x125 µm depletion mode AlGaN/GaN HEMTs with a drain-source (D-S) distance of 3 µm and 6 µm, and the performances of HEMTs were compared. Thanks to these measurements, the performance of the fabrications could be followed and the effect of the distance between D-S on HEMT performance was observed. From DC characterization of HEMTs, conduction resistance, knee voltage, maximum drain-source current, threshold voltage, transconductance and breakdown voltage have been obtained. The results showed that 2x125 µm HEMT with a distance between D-S of 6 µm has higher maximum drain-source current and conduction resistance and lower leakage currents. The obtained results can be explained by the fact that the 2x125 µm HEMT with a D-S distance of 6 µm has a greater gate head length and field plate length than the HEMT with a D-S distance of 3 µm. As a result, it is seen that 2x125 µm HEMT structures with a D-S distance of 6 µm should be preferred for high power applications, and 2x125 µm HEMT structures with a D-S distance of 3 µm should be preferred in high frequency applications. New studies should be continued to obtain HEMTs structures which can operate at high power and high frequencies owing to its low leakage currents, conduction resistance, high maximum leakage current and transconductance. Thus, it is necessary to determine the appropriate HEMT structure with simulations and to come true the fabrication.