Comparison of the DC and microwave performance of AlGaN/GaN HEMTs grown on SiC by MOCVD with Fe-doped or unintentionally doped GaN buffer layers

In this brief, the authors present a comparative and comprehensive investigation of the effect of the type of resistive GaN buffers on the dc, dynamic, microwave, and power performance of AlGaN/GaN high electron mobility transistors (HEMTs). Two types of buffer layers were investigated: 1) a nonintentionally doped resistive GaN buffer and 2) an Fe-compensated buffer. The Fe modulation-doped buffer is shown to be favorable for better dc isolation. The RF small-signal performance of the HEMTs does not exhibit any significant dependence on the type of resistive GaN buffer. However, the type of GaN buffer influences considerably the dynamic large-signal characteristics of the processed AlGaN/GaN HEMTs. The continuous-wave output power density of the AlGaN/GaN HEMTs at 3 GHz was increased from 3.4 to 9.7 W/mm by using a nonintentionally doped buffer instead of an Fe-doped one. Based on this observation combined with pulsed current-voltage measurements, we ascribe this difference to the deep trapping of electrons by defects in the GaN buffer introduced by the incorporation of Fe.