Time Dependence of RF Losses in GaN-on-Si Substrates

GaN-on-Si HEMT technology suffers from RF losses and non-linearities originating from the conductive Si substrate. The understanding and modeling of substrate performance are key to enable next-generation front-end modules. In this paper, we show that when subjected to a chuck bias step, effective substrate resistivity of a typical C-doped HEMT stack shows a dynamic behavior. Using a dedicated setup, stress/relaxation sequences at different temperatures are performed to understand this phenomenon. With the help of TCAD simulations, it is shown that redistribution of charges trapped in deep defects located in the III-N buffer can qualitatively explain the observed trends. Trap activation energies of 0.43 eV and 0.33 eV are extracted from measured data.