Study of trapping mechanisms affecting AlGaN/GaN HEMTs adopting AlGaN back-barriers with different aluminum concentrations

The influence of different Aluminum concentrations in the AlGaN back-barrier on short-channel and dispersion effects of 0.45 μm-gate AlGaN/GaN HEMTs has been studied. Four samples have been tested, one as reference without back-barrier but with a Fe-doped GaN buffer, and three with an AlGaN back-barrier with respectively a 0.5 %, 1 % and 1.5 % Aluminum. Back-barrier devices have lower current collapse with respect to the reference, the latter being affected by trapping at Fe-induced defects and at deep levels induced by residual C. Devices with 1.5 % Al show subthreshold characteristics comparable with those of reference, but 50 % lower current collapse. 1 % Al back-barrier devices show very low drain-source leakage in pinch-off conditions and as a consequence the lowest dispersion effects.