Base zone widening effect
The base width modulation effect of bipolar transistors (or called the base width change effect) is a phenomenon in which the effective width of the base changes with the applied voltage.
The width of the PN junction space charge region is determined by the applied voltage and impurity concentration. When the transistor is in the amplifying working state, the emitter junction is forward biased, the collector junction is reverse biased, and the reverse bias voltage VCB is relatively high. With the increase of the reverse bias voltage, the width of the space charge region of the collector junction increases, which reduces the effective base region width. When the reverse bias voltage decreases, the width of the space charge region of the collector junction decreases, resulting in the effective base region width. increase. Then Ic becomes smaller. This phenomenon that the effective width of the base region changes with the applied voltage is called the base region width modulation effect, also known as the Early effect.