Gummel plot nonlinearities in polysilicon emitter transistors—Including negative differential resistance behavior

The effects of a thin interfacial insulating layer between the deposited polysilicon layer and monocrystalline silicon substrate on characteristics of polysilicon emitter transistors are investigated. It is found that the position of this interfacial layer relative to the emitter-base junction has a crucial influence on the device characteristics. The observed highly nonlinear behavior of the Gummel plot is shown to result from the lacking of the monocrystalline emitter in the substrate. An interface model with trap-assisted tunneling is used to simulate device characteristics and qualitatively good agreement with experiments is achieved. A physical explanation is further given to such nonlinearity and a new regime of negative differential resistance in the IBversus VBEcurve is predicted based on computer simulation.