2-mm-gate-periphery GaN high electron mobility transistors on SiC and Si substrates: A comparative analysis from a small-signal standpoint

In this paper, a comparative analysis has been conducted on GaN high electron mobility transistor (HEMT) technology on Si and SiC substrates. Small-signal characteristics of 2-mm GaN-on-Si and GaN-on-SiC devices have been investigated. Both devices have the same gate length of 0.5 μm. Special emphasis has been put on the temperature dependence of the buffer/substrate loading effects arising from the Si substrate. As a matter of fact, the “cold” pinch-off admittance (Y-) parameter measurement showed significant loading effect for the Si-based device with respect to the SiC-based one. This has been clearly supported by the analysis of the extracted parameters of the small-signal equivalent-circuit model. The model was also validated by simulating active scattering (S-) parameters, which showed a very good agreement with the corresponding measurements. The results of this paper highlight the impact of buffer/substrate leakage currents on small-signal characteristics and the importance of taking this into account during the modeling phase of the GaN-on-Si HEMT technology. The lower thermal conductivity of this substrate increases the internal temperature, thus stimulating more leakage and reduction of the device power efficiency.