Physical Model of RF Leakage in GaN HEMTs on Si Substrates Based on Atomic Diffusion Analysis at Buffer/Substrate Interface

A RF leakage phenomenon in GaN HEMTs on Si substrates is analyzed with taking atomic diffusion at buffer/substrate interface into consideration, and a novel physical model of RF leakage based on the analysis is proposed. The Al or Ga atoms are moved from buffer layer to Si substrate at an epitaxial growth. Then, an acceptor layer with high hole density and an inversion layer with high electron density are formed in Si substrate. As a result, RF leakage is occurred by the low resistance caused from the two layers. The temperature dependence of S22 and resistance of Si substrate are simulated by TCAD with the proposed physical model, and the results are good agreement with measured results. Moreover, the GaN HEMTs with the improved RF leakage is fabricated, and it realizes the maximum drain efficiency of more than 80%.