Avalanche breakdown in HBTs: variation with collector current and effect on linearity

A method for measuring collector-base avalanche breakdown voltage, V/sub bk/, for a range of collector currents, I/sub c/, using fast pulsed-I/V measurements, is described. Variation of V/sub bk/ as a function of I/sub c/ in an HBT agrees with prediction based on device structure. A new equation is proposed for inclusion in simulator large-signal, nonlinear models. The avalanche current is shown to influence device linearity well below the onset of breakdown. We conclude that modeling and control of circuit distortion may require allowance for breakdown characteristics.