The realization of a Ge-GaAs heterojunction transistor with useable gain

A Ge-GaAs wide band gap emitter transistor has been realized that exhibits useable current gain. The method of fabrication and the transistor characteristics will be described. Useable current gains of 15 to 30 are observed in a structure with an n-GaAs wide band gap emitter and a p-n Ge base-collector region at current densities of 1000 A/cm². A typical device to be described has a collector doping of 10¹⁶/cm³, a 1-micron wide strongly graded diffused base with a maximum doping level of /cm³, and a thin emitter doped to /cm³. The attainment of current gain in a structure with the base region more heavily doped than the wide band gap emitter is in agreement with Kroemer\´s theory.