Experimental and Theoretical Investigation of Kink Behavior in C-Doped GaN-on-Si Power HEMTs Under Substrate Bias and Temperature Variations

In this work, kink effect in the output characteristics of carbon-doped GaN-on-Si HEMTs with a gate length of$2.5~\mu $m has been studied extensively. This effect is attributed to a hot electron-assisted de-trapping mechanism influenced by substrate bias. Acceptor-like traps introduced by carbon doping in the buffer layer play a dominant role, as devices fabricated simultaneously on an epitaxial stack without carbon doping do not exhibit any kink, irrespective of substrate bias. Back-gating measurements revealed that charge trapping in the buffer induces a negative potential, which enhances de-trapping and consequently increases the kink effect. After stressing the device with a positive substrate bias of 50 V, the increase in the maximum kink amplitude and dynamicON-resistance (${R}_{\textit {dyn},\textit {ON}}$) is 325% and 63%, respectively. Temperature-dependent studies showed a non-monotonic variation of both the kink onset voltage and its amplitude for biased and floating substrate conditions. Further, crosstalk between a stressed high-power device and a low-power device on high resistive silicon substrate was found to increase the kink effect. An increase in kink amplitude by a factor of 10 was observed after stressing the high-voltage pad at 175 V under floating substrate conditions. In contrast, no significant change in kink amplitude is observed when the substrate is grounded.