High-gain bipolar transistors with polysilicon tunnel junction emitter contacts

Experimental measurements of the dc gain as a function of temperature and of emitter-base and collector-base current-voltage characteristics for bipolar transistors with polysilicon contacts to the emitter are reported, dc gains as high as 2000 have been measured in devices for which a thin insulating layer was encouraged to grow between the monocrystalline silicon emitter and the polycrystalline silicon contact layer. This gain is 20 times larger than that for devices in which the insulating film growth was inhibited. It is suggested that, for these particular devices, the polysilicon layer contributes to a contact which is very similar to that of a metal-insulator-semiconductor tunnel junction contact. A model based on this hypothesis is developed and shown to give a good fit to all the experimental data.