Investigation of hot carrier transport in silicon permeable base transistors

The effects of variations in the source to drain distance have been investigated for several highly doped Permeable Base Transistor (PBT) structures. A detailed study of the hot electron transport in these structures is presented using a 2-D self-consistent full band Monte Carlo (MC) simulation program. The PBT structures considered are the overgrown, etched source and etched drain PBT. Finally we have simulated a structure where both the source and the drain have been etched. All structures have a high doping level in the channel (10¹⁷ cm^-3) and are operating under a gate biasing far from the threshold voltage. The etched structure shows a larger increase in the unity current gain frequency (f_T) than the overgrown structure as the source to drain distance decreases. By optimizing the source to drain distance of the etched source PBT, the f _T can be increased by a factor of two. Our Monte Carlo result has been compared with an ordinary drift-diffusion (DD) model and a more advanced energy transport (ET) model. The difference between the MC and DD model is largest for the etched structures, while it is less significant for the overgrown structure. However, all structures considered in this work, long and short channel devices, show a larger dc current level in the MC model. This is related to the large electric field and high carrier temperature near the gate depletion region