Effect of emitter current on the properties of the collector junction in silicon and germanium transistor structures

We have studied the effect of emitter current on the capacitance of a forward-biased collector junction in silicon and germanium transistor structures. The results demonstrate that nonequilibrium carriers in the collector junction at a nonzero emitter current are responsible for an additional capacitance and facilitate conversion of the net capacitance of the collector junction to an inductance (negative capacitance). Therefore, both the magnitude and sign of the collector capacitance can be controlled by varying the emitter current. Experimental evidence is presented that, at high emitter currents, the barrier capacitance of the collector junction in the transistor structures may both increase and decrease, depending on the nature of the junction and the doping levels in the base and collector regions. Our experimental data agree well with calculation results.