Gummel plot

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In electronics, the Gummel plot is the combined plot of the electric currents $I c$ and $I b$ of a transistor vs. the base-emitter voltage, $V b e$ , on a semi-logarithmic scale. This plot is very useful in device characterization because it reflects on the quality of the emitter-base junction while the base-collector bias, $V b c$ , is kept at a constant. A number of other device parameters can be garnered either quantitatively or qualitatively directly from the Gummel plot: the d.c. gain, b; base and collector ideality factors, nIb and nIc; series resistances and leakage currents.