Electron delay analysis and image charge effect in AlGaN/GaN HEMT on silicon substrate

A delay time analysis is carried out for SiN-passivated AlGaN/GaN High Electron Mobility Transistors (HEMTs) on silicon substrate featuring gate length of 90 nm. The influence of high parasitics in the access pads is considered using de-embedding procedure from the measured S parameters. From the obtained transit delay contributions, the effective electron velocity is estimated to 0.85×10⁷ cm.s^-1. In addition, the effect of the image charge on the drain delay is experimentally demonstrated through the extraction of the mirroring coefficient a close to the predicted simulation value.