Surface accumulation Layer transistor (SALTran): a new bipolar transistor for enhanced current gain and reduced hot-carrier degradation

We report a new surface accumulation layer transistor (SALTran) on SOI which uses the concept of surface accumulation of electrons near the emitter contact to improve the current gain significantly. Using two-dimensional process and device simulation, the performance of the proposed device has been evaluated in detail by comparing its characteristics with those of the previously published conventional bipolar transistor structure. From our simulation results, it is observed that depending on the choice of emitter doping and emitter length, the proposed SALTran exhibits a current gain enhancement of 10 to 70 times that of the compatible bipolar transistor. We also demonstrate that the presence of the surface accumulation layer does not deteriorate the cut-off frequency as observed in the high-low emitter junction bipolar transistors. Our simulations also indicate that when the emitter is lightly doped, the SALTran is immune to hot carrier injection problems due to the reduced electric field in the emitter. The effect of surface states at the emitter contact and temperature on current gain have been examined.