Impact of III-N buffer layers on RF losses and harmonic distortion of GaN-on-Si Substrates

The reduction of substrate RF losses and nonlinearities is key to enable high-performance GaN-on-Si HEMT based RF front-end modules. In this paper, the impact of the epitaxial III-N buffer layers on substrate RF losses and harmonic distortion is studied experimentally using coplanar waveguide (CPW) structures. In contrast to a SiO2/Si stack, a strong hysteresis in the RF losses (quantified using effective resistivity (rho_eff) of the HEMT stack is observed when the chuck DC bias is swept. A comparative analysis of various material stacks suggests that the hysteresis originates from the large time constants (much larger than 1 s) associated with the traps in the III-N layers. Harmonic distortion, on the other hand, shows much weaker hysteresis effect than reff during chuck bias sweep