A high-speed, medium-power, triple-diffused germanium NPN switching transistor

In a double-diffused germanium NPN mesa transistor, the ratio of BVCBOto BVCEOis more favorable than in a PNP epitaxial unit, but when a collector-bulk resistivity (namely 1 Ω-cm) is used that will produce the desired BVCEO, the resulting VCEis intolerable. Since, because of the gross difference between the diffusion rates of n-type and p-type impurities in germanium, epitaxial material cannot be used in the conventional manner to fabricate a germanium NPN transistor, some other way had to be found to easily and effectively reduce the resistivity of the extrinsic collector region in order to overcome the VCE, problem. This paper describes a new and novel technique that accomplishes this necessary reduction in resistivity.