Very high-power transistors with evaporated aluminum electrodes

The principles involved in the design of high-power and very high-power transistors are considered in brief. The important factors in high-gain, high-current transistor design are the emitter-injection efficiency, the emitter and collector planarity, and the base-bias high-current falloff. The fabrication techniques involved in the production of transistors to maximize the injection efficiency and planarity (by evaporation of aluminum electrodes) and minimize base bias drop (by choice of optimum emitter geometry), are discussed. The characteristics of devices capable of handling currents in the range from 1 to 10 amperes at very high common-emitter current gains ranging from 50 to above 300 are described.