A polysilicon base bipolar transistor

We have made PNP bipolar transistors consisting of n and p type polysilicon layers on a 0.01 ohm-cm p type substrate. The object of making this device was to study minority carrier transport through the n polysilicon, although we have also succeeded in making transistors with current gains greater than 5. Preliminary results indicate strong recombination in the bulk base polysilicon, with diffusion lengths less than 40nm. The base region nearest or within, the single crystal substate is much more transparent to minority carriers. In addition, the polysilicon seems to block minority carrier injection from the substrate.