Effect of Polarization Coulomb Field Scattering on Electrical Properties of the 70-nm Gate-Length AlGaN/GaN HEMTs

This research presents the first experimental observation of the enhancement of the polarization Coulomb field (PCF) scattering by aggressive lateral scaling of GaN HEMTs. By decreasing the source-drain distance to 300 nm through n(+)-GaN ohmic regrowth, 70-nm gate AlGaN/GaN HEMTs achieved an extremely low electron mobility. Different from the electron mobility of the traditional device, which was determined by polar optical phonon scattering, the electron mobility of the 70-nm gate AlGaN/GaN HEMTs was dominated by PCF scattering due to the enhanced nonuniform strain distribution of the AlGaN barrier layer. Furthermore, compared with the parasitic access resistance at gate-source voltage V(GS) = 0 V, the parasitic access resistance at V(GS) = −2.5 V showed an increase of approximately 700%, which was also responsible for the enhanced PCF scattering.