A P-N-P Triode Alloy-Junction Transistor for Radio-Frequency Amplification

The performance of alloy-junction transistors falls off as the frequency increases. Heretofore, the chief cause of this has been the resistance-capacitance low-pass filter effect in the base-emitter input. The effect is produced by the germanium resistance (between the external base connection and the active junction region) and the emitter-to-base diffusion capacitance. The latter may be extraordinarily high because of the relatively slow diffusion of charge carriers into the base region which must be charged up and discharged with minority carriers. In the new transistor design of the present paper, resistance and capacitance have been reduced by using a thick wafer of low-resistance germanium and placing the active junctions on a very thin section produced by drilling a well into the wafer. The junctions are about 0.0005 inch apart. Other capacitances are reduced by using small diameter junctions. To prevent limitation due to transit-time dispersion, nearly planar junctions are obtained by using germanm-indium alloy discs from which the junctions are formed. The new unit will give 39-db gain (neutralized) at 455 kc, 12 db (unneutralized) at 10 mc and has an oscillation limit of 75 mc. A noise factor at 1 mc as low as 4 db is achieved.