Operation of poly bipolar transistors near liquid-helium temperatures (9 K)

Operation of bipolar transistors with poly emitters with current gain beta >25 at 77 K and beta >3 at 9 K has been demonstrated. In the temperature range of 300 K to 9 K, the plot of beta vs. temperature (T) exhibits a minimum at T equal to 40 K: decreasing monotonically from 300 K to 40 K, remaining unchanged between 40 K to 30 K, and increasing slightly from 30 K to 9 K. This behavior is attributed to freezeout of acceptor impurities in the base for T>