Gummel plot

The Gummel Plot is the combined plot of Ic and Ib vs. the base-emitter voltage, Vbe, 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, Vbc, 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.