# Gummel plot

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

A number of other device parameters can be garnered either quantitatively or qualitatively directly from the Gummel plot:[1]

• the common-emitter current gain, ${\displaystyle \beta }$, and the common-base current gain, ${\displaystyle \alpha }$,
• base and collector ideality factors, ${\displaystyle n}$,
• series resistances and leakage currents.

Sometimes the DC current gain, ${\displaystyle \beta }$, is plotted on the same figure as well.

SiGe HBT Gummel plot