The influence of Al composition in AlGaN back barrier layer on leakage current and dynamic RON characteristics of AlGaN/GaN HEMTs

In the study, thin AlxGa1-xN back barrier layer (BBL) with different Al composition (x) was employed in AlGaN/GaN HEMTs with GaN/AlN SLs schemes on Si substrate. The AlGaN BBL with low Al content (x<0.15) has no significant effect on the crystalline quality, while a higher Al content will induce more dislocations and cause surface defects. The DC I-V characteristics show that AlGaN BBL (x=0.1 and 0.15) is beneficial for obtaining high I-on/I-off ratio of 10(8) and improving the off-state behaviors with lower leakage current and higher breakdown voltage. The dynamic R-ON measurements were performed by applying the drain pre-bias switching and different quiescent bias pulse tests. It is shown that the AlGaN BBL can effectively suppress the R-ON,R- dynamic degradation, due to that the channel electrons trapped in the C-doping buffer were reduced by mitigating the electrons spill-over effect under the strong off-state bias. However, the device with higher Al-content AlGaN BBL exhibits a rising R-ON,R- dynamic caused by the surface defects related traps. Overall, the devices with 0.1 and 0.15 Al-content AlGaN BBL have an optimal performance.