Excess OFF-State Current in InGaAs FinFETs: Physics of the Parasitic Bipolar Effect

InGaAs FinFETs are challenged by relatively high leakage current in the OFF state. This originates from band-to-band tunneling (BTBT) at the drain end of the channel that is amplified by a parasitic bipolar effect (PBE) as a result of its floating body. In this paper, we present a simple model of the PBE in InGaAs FinFETs, which captures the key gate length and fin width dependences. Our model accounts for surface recombination at the sidewalls of the fin as well as bulk recombination at the heavily doped source. When compared with experimental results, our model suggests that fin sidewall recombination dominates in long gate length transistors and leads to an exponential gate length dependence of the current gain on the parasitic bipolar junction transistor (BJT). The model enables the extraction of the carrier diffusion length which exhibits the predicted fin width dependence. For short gate length transistors, source recombination is shown to dominate and the parasitic bipolar gain scales with the inverse of the gate length.