Gummel plot

In electronics, the Gummel plot is the combined plot of the base and collector electric currents, $$I_\text{c}$$ and $$I_\text{b}$$, of a bipolar transistor vs. the base–emitter voltage, $$V_\text{be}$$, 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, $$V_\text{bc}$$, is kept constant.

A number of other device parameters can be garnered either quantitatively or qualitatively directly from the Gummel plot: Sometimes the DC current gain, $$\beta$$, is plotted on the same figure as well.
 * The common-emitter current gain, $$\beta$$, and the common-base current gain, $$\alpha$$,
 * Base and collector ideality factors, $$n$$,
 * Series resistances and leakage currents.