Interpretation of the common-emitter offset voltage in heterojunction bipolar transistors

The offset voltage in heterojunction bipolar transistors (HBTs) can be read graphically from a plot combining the forward Gummel and reverse Gummel plots. We use a Gummel-Poon model to show when this graphical construction works, and illustrate the method with measurements for InP/InGaAs double HBTs.