Operation of sige HBTs at cryogenic temperatures

The operation of SiGe HBTs at cryogenic temperatures is investigated experimentally and theoretically. It is demonstrated that the collector current at cryogenic temperatures is caused by electron tunneling through the base. The temperature dependence of the transistor characteristics reveals a transition from conventional thermally activated transport at room temperature to tunneling dominated transport at cryogenic temperatures. Experimental results are presented for HBTs with a peak current gain of 8000 at 300 K and 45000 at 10 K.