An investigation of the dependence of the current gain of a plane-alloy-junction transistor on emitter current and frequency

The complex internal current gain, ¿d, of a diffusion-type germanium transistor has been derived from measurements of the external short-circuit current gain, ¿, at frequencies up to 20 Mc/s and for emitter currents between 15 ¿A and 3 mA, by taking account of the effects of the emitter and collector depletion-layer capacitances and the ohmic base resistance. The resulting frequency dependence of ¿d is that expected from unidimensional diffusion theory. At low emitter currents, the flow of r.f. current in the emitter depletion-layer capacitance causes the cut-off frequency of ¿ to be less than one-third that of ¿d.