The Frequency Response of Bipolar Transistors with Drift Fields

The frequency response of bipolar transistors is calculated using a model which assumes that the spread in the transit time of minority carriers flowing from emitter to collector is the major factor in determining the frequency cutoff. The total emitter-to-collector transit time is determined by the combined effects of drift and diffusion but the spread in transit time is determined exclusively by diffusion. The analysis is adapted to point-contact transistors and checks experimental measurements of frequency cutoff in four groups of point-contact transistors having different structure and material parameters.